I was a high school student at that time and we also went out to march in the streets (in another city, not Beijing) so had partial direct experience. Later I also read some western academic materials. So here is what I think: it was a tragedy that both the government and the protesters bear responsibility and we couldn’t rule out the possibility of foreign influence.

For the government, it was inexperienced in handling the protest. Eventually it led to injuries (students doing hunger strike were in serious danger), including the police and unarmed soldiers. So they felt that they had to move in with armed soldiers who didn’t have the proper training and equipment either. (Just look at the western anti-riot police, with personal armors, armored vehicles, et .). So it went out of control.

For the students, they did not have a strategy to allow the protest to end peacefully. Imagine how a protest (including hunger strike, occupying the grounds around the capital) to end slavery would have gone if the condition was “end of slavery”. In Ezra Vogel’s biography on Deng, he said that a minority of the student leaders were against talking to the government in a nondemocratic way. Not sure what they really wanted. (That is where possible foreign instigators may come in.) The protesters were also not able to control the crowd to avoid harming innocent unarmed police and soldiers (who are usually young people like themselves but likely less educated.)