For example, if a new member buys an account because he want to trade in Bitcoin, then he will probably get a red tag, and this is despite the fact that he has not breached any of the forum rules.
There's no reason why anyone would have to buy a bitcointalk account in order to trade bitcoin. Jet Cash, you've been here long enough to have read all of the explanations as to why account dealing is toxic to the forum and thus why those who engage in buying or selling of accounts get tagged. If you don't agree with that, don't tag 'em. Me, I'll still be happy to. There are exceptions, of course, and I don't think every single account seller is an evil person or even has bad intentions necessarily, but this is one of the issues where the forum rules haven't caught up to community standards--just like scamming, which isn't tolerated either.
Edit:
I think account selling should be banned - it is on most forums.
I agree with this completely, but like I said it's a case of the forum rules not reflecting what's acceptable practice here, which is why DT members have stepped in. I've got nothing against alt accounts per se as long as you're the one who created them from the start. The problem with buying an account is that the account's reputation/rank/merit history/etc. doesn't reflect anything the new owner did and that new owner could easily try to deceive someone when asking for a loan, trying to buy bitcoin, selling something, and probably a lot of other things. If someone got their hands on an account with green trust, it'd be very easy to scam someone.
Anyway, we're probably on the same side of the issue so I don't feel like writing a huge essay condemning account sales. I've done that before, and I'm sure you've probably read a few of my rants. Theymos isn't likely to prohibit account sales anytime soon, so tagging members engaged in that activity is really the only thing that can be done to discourage the practice.