Whether it's China or really anything, I'd agree to being critical of any claims made without proper context, yet the context here is the massacre and subsequent cover-up perpetrated by the Chinese government following peaceful protests on the Tiananmen square.
Meeting that with whataboutisms and vague excuses is disrespectful towards the victims full stop.
Being a socialist should be easy, because truth is on our side. It should be easy to point to Tiananmen square and say "this is what happens when the ruling class feels threatened", just like you can say the same thing when the US government busts their unions or murders their black citizens. Being an unquestioning supporter of either of these regimes is not what socialism is to me, and it never was. I just don't understand how anyone can reconcile these opposing views in their heads.