I disagree. No one is trying to ban him, and his threads in the wrong boards haven't even been deleted. He's being allowed to spew his nonsense anywhere he goes. Negative trust does not stop him posting in any way shape or form.
Similarly, there are no free speech restrictions on trust, which is why most DT members have a plethora of ratings calling them pedophiles, racists, motherfuckers, faggots, whores, etc.
Usual 'untrusted' ratings barely have any effect, while DT members have the power to render accounts almost useless for plenty of activities on the forum.
He can continue writing, but users who share unpopular beliefs are now more afraid to express them, knowing there's is a possibility they will get red-tagged!
That's why it's a threat to discussion.
That isn't a battle of ideas, an argument, it's use of power in order to intimidate and silence.
It doesn't matter it's about flat-earth, it starts a bad precedent.