That doesn't mean that everybody who believes bad ideas will be persuaded. Obviously that can never be true. But when bad ideas are suppressed, those who hold such opinions feel persecuted. And persecution lends the bad ideas an aura of rebellion or legitimacy, which attracts new followers.
Think about it. If all racists are banned from all mainstream websites and all mainstream registrars, where these racists were in the minority, then what happens? The racists will congregate elsewhere, where they are in the majority. If some suggestible 18-year-old is undecided and walks into a room, then it makes a big difference whether the room is 90% racist or 1% racist. On Facebook, perhaps, the racism would be rebutted by the 18-year-old's friends and fail to spread. But once Facebook bans racist views, then the kid will find that racism in a much more concentrated form on some other platform where it is expressed in much more extreme ways. And there nobody will rebut the dumb racist opinion. So it will seem more plausible. Add to that the allure of having been banned by all the major platforms, and it's no wonder that some naturally rebellious teenager or disgruntled middle-aged dude finds satisfaction and a sense of belonging by participating in a gang of too-dangerous-for-mainstream folks who know the secret truths that "The System doesn't want you to know".
The remedy for the spread of bad ideas isn't to continue de-platforming and suppressing and censoring them until they end up super-concentrated. If you ask me, it's the opposite: Let offensive ideas be expressed in the person's normal social circles and on normal online platforms. That is where those ideas will be challenged in the MAXIMUM way. This dilutes and dissolves most of the bad ideas.
how often do people post really bad stuff out in the open on facebook or twitter, giving their more normal friends and family the chance to argue with them? like the worst things you might see on gab? most people know that has the potential destroy your life.
even if people did, there would probably be a lot of animosity directed towards them, not empathy and sound arguments. then they would likely stop..or continue and lose a lot of respect.
that could push them away too, to other communities.
most of the internet isn't just some kind of public square where everyone is out in the open, engaging in somewhat civil dialogue.
but anyway, people can always make other accounts to interact on bad facebook pages and groups, follow crazy people on twitter, and tweet whatever they want.
they can ignore the few dissenting voices who happen to engage on their crazy twitter feed. there's not really a way to have a good discussion there anyway.
the big social media networks aren't full of patient and empathetic people with rational arguments.
there's a lot of good information to be found, but it's often overlooked or ignored.
if social media was like a public square where everyone was interacting with everyone else, and people usually interacted with civility, and all the best arguments and most convincing evidence were in plain view, then it might be fine to allow hateful racists to have their "booth" in the square, next to everyone else's booths.
(not that a public square is the solution. the majority of the citizens could still end up being idiots who are swayed by the flat-earther or racist. I guess the solution is a good education system, but some would probably whine that it's "indoctrination", because they don't understand what good education is. maybe just getting people to read good books too.)