In Russia, national troops were motivated to fire upon citizens of their own country in the context of more or less peaceful protests for fairly basic human and working peoples' rights because those participating in the protest represented an existential threat to the divine autocracy of the Romanov dynasty, which they were sworn to defend. These protestors and their sympathizers had been so severely smeared for so long that they had come to be perceived as traitors-- despite the utter absurdity of that assessment. They were no longer worth saving, they were vermin to be removed, a blight. Holy Mother Russia was at stake. The indifference and brazen scorn with which the aristocracy related to the lower classes made this attitude inevitable and as violence increasingly became the only outlet for disaffected Russians to achieve representation in their government, they used it more and more. This only served to exacerbate the tensions between both sides and confirm everything the loyalist troops had been told in the first place.

The absolutely key factor was the mental decompartmentalization of the left by the right and the right by the left. Every protester was a Socialist Revolutionary. Every loyalist was a member of the Black Hundreds. Put two large groups of people together who have dehumanized the people standing across from them so severely, add in some over-powered commanders eager to earn favor with the autocrat (who personally stayed as far away from such decisions as possible) and are you really surprised at the results?

Russia was in troubled times long before Bloody Sunday and Nikolai II though, and it's not as if the loyalist troops did not have plenty of reasons to view protesters as violent elements-- Nikolai II's grandfather Aleksandr II had been killed by an assassin who lobbed a bomb at his feet after he had gotten out of his carriage to accost a different assassin who had tossed a different bomb at him moments before. Aleksandr II was one of the most reform-oriented emperors that the Romanov dynasty produced. His father (Nikolai I), on his deathbed, had made the young Aleksandr Romanov promise to destroy serfdom (chattel slavery of the Russian variety-- you are not free, your children are not free, you can be bought and sold), and abolish it he did, freeing literal millions of Russians to move to cities like Saint-Petersburg to work in the newly growing industrial sectors.

Aleksandr II's son and successor Aleksandr III had been attacked many times as well, once by a group which had included Aleksandr Ulyanov (albeit in the role of bomb-maker, not assassin), older brother of Vladimir Ulyanov who would go on to don the revolutionary nom de guerre Lenin. Aleksandr's hanging was a crucial inspiration for the young Lenin to pursue a revolutionary career in the first place.

Growing up amid such open hostility for the divine rulers of Russia, and despite all his supposed personal weakness, one area where Nikolai II would almost never waiver throughout his entire career was his God-given right and duty to rule the Russian Empire from a position of complete autocracy-- no constitution, no parliament, no oversight, no ministers. To limit the autonomy of the emperor would be to limit the autonomy of God's will. To the Russian noble D.P. Svyatopolk-Mirsky, Nikolai II once remarked:

You know, I don't hold autocracy for my own pleasure. I act in this sense only because it is necessary for Russia. I'll never agree to a representative form of government because I consider it harmful to the people whom God has entrusted to me.

That just about sums up his entire reign. Very little pleasure derived from a duty he inherited against his will, which required that he hold together an empire that had been imploding since his namesake Nikolai I had put down the Decemberist Uprising in 1825. Of course the big difference now was that instead of trying to halt a revolution in a world where the telegraph, automobile, and typewriter had yet to be invented like Nikolai I, Nikolai II was trying to do so in the world of stock markets, industrialization, and organized Marxism. When your interlocutor is negotiating from a inflexible position and you are as well, as they say, something's gotta give.

Many of the reformers within the Russian Empire were attacked as Jewish cabalists, Emperor-hating, anti-Nationalists, and anti-Christians. The rallying cry of loyalist elements in the Russian Empire was 'Tsar, Faith, Fatherland.' On the supposed propensity of Jews to participate in revolutionary and subversive activity then-Prime Minister Sergei Witte (whose own philo-semitism resulted in his ouster from governance) said:

It seems that at least 50% of these revolutionary groups throwing bombs are composed of Jews, probably because of their oppression by our government. Perhaps if I were a Jew, I'd be among them, throwing bombs myself.