There's also the case in which you suspect a user of scam, but have no proof of it, who decides on such cases and where would the line be drawn?
Speaking purely from my pov, ban should be reserved for well documented scammers like 1xbit (and for exactly that reason their banner bid was refused) and not just anyone with a negative tag given by a couple of DT members when they suspect someone
might be a scammer, or something along those lines. So, I don't think it would be good to go completely wild and remove anyone suspicious (like they are often doing on some other forums) but should be reserved for those rare cases.
I understand the argument that moderating scams would help in the very least to prevent proven scammers from posting on the forum, but the can easily create new accounts and continue with a new identity or shift their focus to other social platforms by attracting their victims to telegram or discord.
So let scammers go there. Telegram is a known cesspool, bitcointalk doesn't have to be.
edit:
Some things are not moderated like scam, trust system, merit system but there are many things that are moderated because forum have admin, staff and moderator who carry out their respective function. Do they deserve to be called a central authority where they can do several things for the forum community such as moving thread, deleting post, merging posts to ban users? If I misunderstood the central authority you mean, please clarify.
He probably referred to trust system when saying that its without central authority, I also misunderstood that part of his post at first.