During years, twitter (/facebook) gave a platform for free hate speech talk and didn’t moderate. And twitter became too big to be able to moderate its platform.

That’s true, twitter could have done something, but they didn’t…

My opinion is that the fediverse will make those extremists become unheard again as most instances will ban the few “free hate speech” instances.

I am not that optimistic that hate speech instance will be few and easy to ban, but I am optimistic that the tech will be able to come up with clever ideas to find a mix between white and blacklisting new instances. Maybe a trust system or something like that will help.