Nothing, prison is a warehouse. Remember though all that occurred was property damaged and a level of intimidation that would make a person of sturdy character laugh, on the spectrum of political action it really was not that extreme
The intent was for the intimidation to work, so regardless of how sturdy the character. Its hardly a victimless crime.
Marching and demonstrating maybe not as effective, but I find it hard to celebrating trying to harm another person, regardless of how ineffective. Non-violence is a good way to change unjust laws, intimidation is not just.