Certainly other platforms are free to censor as they please, but they may do so to the detriment of developing a healthy community where new and valuable ideas can be forged in battlefield of a good discussion.
Why certainly when one wants to exercise their free speech they have to create their own platform, open platforms provided by internet that facilitate communication is a good thing. And open platforms and ideas tend to flourish as time goes on.
I will disagree on the violence thing, however. Unless someone is threatening your safety or the safety of another person directly, you should never use force because someone says something you may disagree with. Are there people that use violence? Absolutely. But when someone offends someone in a way socially inappropriate and that person uses violence, the person using the violence is committing the worse action. If that person didn't use violence, then society has ways of isolating people who take free speech too far. But no one should be prevented from speaking on the basis that they might get hurt because it may offend the wrong group of people. Because some people get offended at the tiniest things and we shouldn't be intimidated by them if what we are saying is something we believe in.