First, units of evil are given to IPs which have perma banned accounts, however scammers won't be banned, only spammers do.
I don't understand this point, I never suggested scammers should be perma-banned. I'm suggesting a change to the system.
Second, you said that the user will get evil units according to trust score, but according to which calculation? Everyone use different trust list (with most being depth 2), and hence different trust scores will be shown to different users. So this is not a good method.
DefaultTrust. I should've made that clear, but if we're getting into the "blehh DefaultTrust is inaccurate and centralized!!" argument again the thread should diverge.
1) This would in effect, cause scams to be somewhat moderated which is something that the forum is strongly against.
I get your point, but I don't agree this is moderation. This is keeping the trash from returning over and over, and it's not necessarily just for scammers.
2) There are several examples of people receiving negative trust (sometimes from multiple people) when there was not really any kind of scam
If you're referring to false negative trust, then this usually gets sorted out. If you're referring to negative trust that was for untrustworthy behaviour, then that's still fine. My proposal is for keeping the trash out in general, not just scammers.
3) This will potentially allow serial scammers to avoid detection because they will know right away that they are associated with their previous account who was caught scamming, so they can try new/additional things to avoid detection until they do not have to pay a fee. This is important because it is very rare that very new users will be able to scam, as you generally need to build it up a little bit, which takes time, so while it is being built up, it would be possible for BadBear to send it negative trust to warn others.
That is a valid point, but I feel that anyone who would do this is already doing this.
I feel there's a slight conflict of interest in what you're saying, too, due to your own trust score and actions.