Twitter has a (undeserved and unjustified) name as The Place to hear what people have to say, to hear the opinions of regular people, where big announcements are made, etc.
Journalists and politicians have favored it and despite its user base still pretty much being pretty limited it has a far outsized influence on things. Compare and contrast to FB which, despite its multitude of other failings, can actually up to a point state they can reach the vast majority of normal people in the western world.
Twitter allowing or even supporting hate speech, lies, propaganda, etc will poison the well of public speech and public opinion even further.
It wasn't great before, definitely, but it will get even worse.