The same way a store can't kick someone out who's running around saying racial slurs to everyone?
The same way the New York Times is required to print every letter to the editor that is sent to them?
The store example doesn't hold up at all for a number of reasons and online communities have had extra legal standards since the beginning of the internet.
They can't kick out whoever they want, governments regulate that. And here Germany decided that Youtube can't kick out people for a particular reason. It is the same concept.
They can but not because the store has negative opinion about this behavior but because that behaving disorderly in public place is against the law. Actually they should just call the cops.
In America at least, there are different sets of rules for different types of business.
A curated opinion piece, carefully chosen by experienced editors, is vastly different from a public swimming pool. For the first, that filter, that exclusivity, that editorializing is part of the draw. It’s good because it’s a filter, not a platform. The public pool should not be a filter, and yes, sometimes there are weird things that float in there, and it takes effort to clean up, but that’s the cost of being open to the public.