I can't give you much on American public opinion, but I can address your third point.

In the few years of division before war (1945-50), North Korea implemented a lot of really popular policies. This included land reform that parceled out property to the common people; empowering women to work outside the home; schools and daycares; and public work projects. At the same time, South Korea was busy attempting to stamp out leftists and prevent a left-leaning state from springing up and ousting the pro-American dictatorship in place.

After the war, South Korea was still a dictatorship attempting to stamp out leftist opposition. Remember, this is the height of the Cold War. Priorities being what they were, the leadership in South Korea was more concerned with maintaining power than rebuilding. North Korea, with the support of both China and the Soviet Union, was able to immediately turn attention to reconstruction. South Korea remained under dictatorship/military rule for decades. They didn't elect a civilian president until 1993. It's difficult to imagine, because South Korea today is a massive developed economy, but North Korea was doing objectively better for a long time.

The cult-of-personality didn't really begin until the transition of power from Kim Il-Sung to Kim Jong-Il. While the elder Kim had legitimate credentials for leading the party and the state, Kim Jong-Il... not so much. So the veneration of Kim Il-Sung was designed to legitimize Kim Jong-Il's succession. That amazing state education implemented in interwar years turns out to be a perfect vehicle for indoctrination. The economic descent of North Korea is more linked to the winding down of the Cold War: without the Soviet Union and China providing resources and manpower, North Korea's economy stuttered. The country became isolated from the global economy (the same global economy that finally pulled South Korea into Asian Tiger status). This was followed by a famine in the 1990s and the collapse of the state distribution system. North Korea hasn't recovered.

It's hard to imagine how sudden this shift must have seemed. Imagine someone born in Korea, say, in the year 1910. This person is born the same year that the Korean king is ousted, and Korea annexed into the Japanese empire. If they were left-leaning politically, they might go to China in their late teens/early twenties and fight in the Chinese civil war, or perhaps join an anti-Japanese guerilla organization. Age thirty-five, their country is split in two, and they probably have relatives on either side of the border. Age forty, open war between countrymen. The literature from this period is heart-wrenching. Some parents had children fighting for opposing sides, and loyalties were divided.

After the war, if this person is in North Korea, they enjoy an adulthood of fairly secure living, with work and education and land to own. But by the age of eighty, this person will have also seen their grandchildren starving to death, and their children possibly hauled off to re-education or work camps.

If this person is in South Korea, they will have watched as Americans slipped into old colonial institutions and continued the persecution of leftists. They will have worried about getting work and getting food; education is a luxury. But by age eighty, they will have seen successful democratic protests, and seen their grandchildren buy cell phones, and go to world-ranked universities, and never worry about food.

Twentieth-century Korean history is fascinating. So many changes within such a short period of time.

Some random thoughts inspired by the video:

• I disagree with the characterization of Kim Il-Sung as a "Soviet puppet." He was an anti-Japanese guerilla fighter prior to the war, with combat experience in China, and solid socialist credentials. There was significant friction between Kim and the Comintern in Russia, which is probably best exemplified by the obvious example given in the video: Kim Il-Sung was intent on unifying Korea with or without Soviet approval. And he made the attempt without Soviet support. During rebuilding, Kim Il-Sung often played China and the Soviet Union against each other to gain benefit. Hardly a puppet; he played his role to his own advantage.

• I really appreciate that the phrase "Northern aggression" wasn't used to describe the invasion. While North Korea's invasion is undoubtedly the spark for the war snowballing into a Cold War proxy conflict, it helps to consider the context. Skirmishes had been on-going for months. Both sides were actively calling for unification by military means. North Korea was flourishing, supported by powerful allies (China, Soviet Union), and was implementing the promised policies that people had wanted under Japanese rule. From the northern perspective, South Korea had exchanged one colonial rule for another, and were no better off for it. It's inaccurate to paint North Korean motives as simple aggression. And I wish that was more well known.

My sources:

The Korean War: A History by Bruce Cumings This is the book on the Korean War, one of the earlier "revisionist" academic works. It might give some insight into American perceptions of the "Forgotten War." It's the book that I would recommend to anyone wanting to get a decent overview of the Korean War, because it addresses the issues with American scholarship (i.e. it's very biased about socialism).

"Everyday Life in the North Korean Revolution, 1945-1950" by Suzy Kim This looks at the interwar years in North Korea, with particular focus on land reform, education, and women.

"The Destruction and Reconstruction of North Korea, 1950-1960" by Charles K. Armstrong This looks at the socialist "fraternity" of states, and how Chinese/East German/Soviet aid was integral to North Korea's rebuilding and economic success in the immediate post-war period.

This entire issue of Cross Currents on "(De)Memorializing the Korean War: A Critical Intervention" is a useful look at how different players recollect the war in the aftermath.

If you can find it, I also recommend "Socialist Korea: A Case Study in the Strategy of Economic Development" by Ellen Brun and Jacques Hersh. It was written in the 1970s, and might give an interesting perspective on how people were explaining North Korea's progress at the height of its success.