It did work. It worked great. It got rid of so much bigotry in our society, and other societies. Indeed, it kept going longer in some other countries, and got rid of more bigotry there.
Bigotry will always find a platform - I outlined the power of forbidden fruit. By denying platforms, you give bigotry more power. Which is what we've seen since the platform-denial started. An increase in bigotry rather than a decrease.
Some people just gave up on persuasion because it's difficult and requires working on ones persuasive skills, honing diplomacy, critical thinking, looking at which argument work better than others to persuade people, honestly listening to other people, and a host of things which are harder than they sound.
Again, the goal is not to persuade the other person making arguments. The goal is to persuade the larger audience to lean more towards your argument. If the other side's arguments are not in good faith, that makes persuasion easier. Let people see their bad faith arguments. Give them the platform to demonstrate their arguments are weak relative to yours. Don't deny them the platform to speak - that just sends the message you fear their message, and that it's stronger than it is, and that you don't want people to hear it for fear their argument will be more persuasive than yours.