In what cases is censorship good?

i personally think censorship is BS and it is done by people in power to keep themselves. to me there is no denying that censorship can be a good thing . an example is something that happened on may 5th. as many of you know, 5 de mayo is a day that celebrates the indepence of mexico from the spaniards. going back to the topic, a few extremists were holding up the american flag in a high school as if to say "this is america. if youre going to celebrate that here just go back to your country". if i am correct those flags were taken away and those people were arrested. had this not happened, there might have been a fight between them and the mexicans who were celebrating the holiday.