That fallacy is basically based on the idea that: A is bad, hence A is false. But that's fallacious because desirability is not connected to truth/falsehood.
I accept your correction.

Nonetheless, your argument is still invalid because it's a False Dilemma.
Your argument "If they had not used military force, the result would been far, far worse" reduces the options to just two (either military force or something "a thousand times worse"), when there were, in fact, other possible plausible outcomes.
Try again!
Your argument still amounts to nothing but conjecture on your part. There were plenty of alternate courses of action (and possible outcomes). The fact that some of the reforms the students were asking for have since been taken up by the gov't without the consequences you predict rather tarnishes your argument.

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