First of all, we cannot controll banned users making new accounts. We do what you mentioned junking topics/posts etc from banned members but that doesn't solve anything.
And secondly and most important, there are way more serious reasons of bans than flaming, xdem, kara and some other users are banned for flaming, but there are scammers that scam every day and we cannot do a lot of things about it, there are users bulling other members and they're doing it by following rules (doesn't scam, flame, etc) and way more reasons that our forum is what it is right now with zero new shares and zero creativity.
Some users flame or act childish but tbh isn't so much harm than other users bulling and scamming people here.
The fact that xdem will write on l2prideful's topics that the server is trash it won't harm his server AT ALL.
But users saying the code someone shared is crap, the npc he made is ugly af, etc will harm the people trying to crete new things and share them with everyone.
The point is, we're at a point that we (the staffers) cannot do a lot about these situations, if members won't change their attitude baning them all will end up worst than having them here and won't change a thing.
If you remember the old days when tons of people got banned for stupid reasons such as staffer in a similar forum, spaming, flaming, etc (ofc i'm not speaking about scammers) ended up making a dead forum because these were the people that would bring activity into the forum. Now we're trying to bring activity using other ways like hidden content and people still bitching and not following rules at all but no one cares about that, you only care about a harmless post of a guy saying trash a server.
My opinion about new accounts > new accounts > new accounts...
In case of permanent ban, the member will lose any right to his topics and the administrator / moderators will have all the right to manage your topics.