It's not even about whether it's effective short term or long term. It's that sometimes the "good guys" have more power, and sometimes the "bad guys" have more power. How you define each of those may differ, but if you allow the group in power (either politically or socially) to suppress/deplatform the opposite group, when the "bad guys" gain power, you're gonna have a bad time.
It blows my mind that Trump's presidency and war on the media hasn't tipped people off that maybe, just maybe, freedom of speech is there to protect you, too, not just the bigots.