I have never seen any source that suggested that the Soviet's industrialization during the two Five Year Plan period were "unethical" in any shape or form. The Soviet Union passed a law limiting work hours to Seven Hours a day, well ahead of both the United States and Britain at the time. The work place safety was no more egregious compared to other industrialized countries. Therefore it is hard to say or even suggest that the Soviet Union had an unethical industrialization in regards to the workers. The Soviet Union provided legally a shorter work week than the United States or Britain at the time, while industrializing at a breakneck pace.
The issue with the Industrialization of the Soviet Union during the first two Five Year Plans was not the industrialization or the working conditions within the factories that sprung up throughout the Soviet Union, it was the societal cost elsewhere in the Soviet Union that allowed such advances to occur so very quickly. In order to literally feed the workers within the new factories that were being built everyday throughout the first five year plan, it meant that agricultural production needed to be controlled, managed, and expanded. This led to death of millions during the 1932-1933 Famine, with the exact number being estimated at around 3.3 million according to Timothy Snyder. The famine can be tied directly to the Soviet Union's desire for quick industrialization, while not being the only reason for the famine. It caused massive movements of people in the Soviet Union.
The industrialization also did not lead to a marked improvement in the average Soviet citizen's life. The long term effects were not felt by those who were the ones working, instead it would take years for the fruits of their labor to be felt. The first Five Year Plan focused mainly on Heavy Industry which allowed, for example, more tractors which ultimately led to more food production by less people, yet it would take years for the effects to be felt. A shortage of consumer goods would also plague the Soviet Union during this period where shortages were common. The industrialization was good for the Soviet Union, but perhaps not good for the individual during that period. The long term benefits, however, cannot be understated either. The Heavy Industry drive did allow the Soviet Union to increase its focus on its military which led to an increase in tanks and weapons being built, which would allow it to protect itself against threats that were very real and would strike by the end of the decade.
Industrialization is messy. It upends the entire society and social order, which leads to fractures and dissent as people are forced from their normal roles and into new ones. Yet long working hours and lack of regulation was not a cause for concern when discussing the Soviet Union's two Five Year Plans. Instead, it was the brutal treatment on the countryside in order to fund and feed the industrialization at an arbitrary scale and speed that is the tragedy and one that is not easy to justify on any measure.
Hi there. Could you clarify what you mean by "unethically?" Was that a typo or did you mean to ask that in your question?
Professor Stephen Kotkin answers this question in his series of biographies on Stalin. He is a geopolitical oriented professor that dispels many myths about Stalin and his contemporaries, I highly recommend his work.
First, it is important to understand that WWI ravaged Czarist Russia's economy in food production/distribution, war production, and consumer goods production. The levels of the latter two would almost never be above half of pre-WWI production until after Lenin's death. Moreover, Czarist Russia has been considered largely inefficient as it engaged in a command economy without the necessary governmental apparatus to organize it. It is just important to know that the USSR started in dire straights.
There are three things that all effect each other in why the industrialization proceeded in such an "unethical" way. I say unethical in quotations because of millions of people died, with a majority in Russia experiencing malnutrition due to these three oversimplified reasons.
Stephen Kotkin shows in his book that it would be a mistake to not consider any of the above three leaders as anything but devout Communists, and that is reflected in their economic policy. When the party first gained foothold in Moscow, it engaged in complete Socialism. They initially banned almost all private trade, using trade unions and government commissariats to attempt to restart factories under a quota system, while also using the military to requisition grain from the countryside. The grain requisitioning was constantly violent and threatened to cause peasant uprisings in a desperate civil war against the Whites.. Even after the war, it sparked a full blown peasant rebellion in Tambov. Huge underground markets formed for both the countryside and city, as city dwellers experienced extreme shortages. Eventually, Lenin conceded to establishing market based concessions called the New Economic Policy. The NEP allowed small private trade with peasants while establishing a tax for production and trade. The NEP alleviated many of the immediate problems, but was heavily criticized publicly by Trotsky, and privately by Stalin. Even Lenin felt forced into passing the concessions in order to save the party. Ultimately, the USSR started to rely on international trade of agricultural goods, which required diplomacy.
A siege mentality was developed within the USSR along with the need to open up relations. Stalin had wanted trade and relations with the rest of the world after immediate world wide revolution had failed. Lenin's war in Poland had been lost, Germany had a failed Communist revolution, and the Chinese Communists had been massacred. The USSR on one hand treated other nations as imminent enemies, and attempted to foment revolutions across the globe. While on the other hand, they wanted to establish trade, credit, and legitimacy with these same countries. The USSR heavily relied on foreign imports of consumer and military goods, that were bought by exporting agricultural products and raw resources. They eventually found a reliable buyer that was also alienated from the rest of the world powers, Germany. Russia needed to import the machinery necessary to build and industrial base to produce war material it needed to protect itself.
The USSR and Stalin felt a constant anxiety of plots by Capitalist powers. That anxiety had some merit. Certainly Britain, France, and America would have preferred no Communism, but these countries were tired of war. However, they still sent forces to aide the Whites in the Russian Civil War, while not actually fully backing those forces. More anxiety was made during various embarrassments of the Red Army. Such as the ease in which the German army almost reached Moscow in WWI, signing a peace treaty at the last minute. Then the Russo-Polish war being a colossal disaster, ending in a Polish victory, despite Poland being a brand new country. Moreover, Japanese had basically occupied the far Eastern parts of Russia for an extremely long time. Finally, despite being on the Entente during WWI, the USSR was divided up and treated as if it had lost the war. Relations however, suffered far more from the self-fulfilling Marxist worldview.
Most major set-backs of the party and Stalin's own personal power was attributed to some kind of Capitalist or Czarist plot. The Krondstat rebellion was viewed as Czarist supporters, despite being real aggrieved communists. Almost every single enemy of Stalin and Lenin, including socialists in the provisional government and party members, were seen as operating on behalf of Capitalist or Czarist powers. There was a real anxiety and paranoid that permeated every facet of the party, and also, was the mechanism in which Lenin and Stalin used to force the party into line. It was an integral part of the Communist government, and it was not conducive to international relations.
Capitalist powers were thought of as only engaging in diplomacy because they were forced to or in their cynical desire for more markets, but that they would attempt to overthrow the party if possible. Therefore, the USSR only ever treated diplomacy cynically. The USSR would be funding and encouraging a strike in Britain, while also trying to engage in diplomacy to gain trade and credit. Britain would however crack their communications and discover it, leading to a break off in talks. What was worse was that the Capitalist powers expected the massive Czarist debt to be paid off, and would only trade or loan on promises to pay that debt off. Whereas the communists viewed that debt as invalid, due to it being the Czars debt and being based on capitalist practices.Difficulties like this limited the USSR's trading partner's. But there would be eventually one to trade with them, Germany, and especially, Hitler. That trade was however bought with agricultural products from a peasant population going through a continuing revolution.
The peasant revolution started as the Czar's power waned. As the peasants gained their independence, they started to confiscate land and form local governments and communities to govern themselves. The Red Army would be surprised when it traveled out to the country side as peasants fought with local landlords, seeing places turned into warzones. It was the army's job to go confront the peasants and force them to turn over their grain, however much the army needed. This practice quickly became hated, and skirmishes would break out with the Red Army, with peasant bands formed to defend their produce. Needless to say, none of this was good for crop production and distribution. However, the NEP was passed, and peasants could engage in private trade if they paid a tax. This solved many of the immediate problems, but Stalin would reckon with it in time.
Essentially, Stalin viewed peasant independence as an eventual time bomb for the party. The independence would hurt the party as consumer goods became scarce due to the aforementioned restriction of trade by Britain. As consumer good became scarce, peasants felt encouraged to save their grain for a time in which their money could buy more. However, this action only limited the USSR's ability to purchase consumer goods overseas, because international trade was solely organized by the party. It also limited the machines needed to build up industry to be able to produce its own consumer goods. Giving in to more concessions was viewed as only encouraging the peasant behavior. Stalin then decided against almost everyone to move forward with enslaving 100 million people.
Stalin would set in collectivization to force the peasants into a command economy. First by eliminating the richest class of peasants called Kulaks in a massive scapegoat for the USSR's problems, and then using the new influence and terror to force farmers onto massive collective farms. The collectivization occurred during a famine, most of it caused by the elimination of the Kulaks, and the collectivization was initially inefficient due to the massive change and destruction of property by the peasants. He then exported grain to build the heavy industry needed to maintain a massive army, causing even more famine. What resulted was one of the worst man made famines ever, killing millions of people in one of the previously largest grain exporters in the world. As far as deeper causes of the inherent concentration of power, or other theories around the evils of Socialism, that is a different discussion.