I hope you are not the person who thinks we should kill every thief.
Temporarily banning automatically spamming users doesn't make much sense. But that's not very harmful anyway, as spammers don't usually reuse their accounts if they were banned once.
But there are many other possible bad behaviors, which are generally much better than spamming. A permanent ban is less meaningful than a temporary one if the user can register new accounts easily anyway. Disadvantages of a permanent ban includes:
- If the user always use the same account, other users may recognize them and not take those things seriously. And if they use different accounts without a reason, the likelihood they are doing bad things increases. You made a reason for them to waste more other users' time.
- If they lose everything they get in your community, they can't lose anything more. A permanent ban makes them no longer need to care about how you think, and may make them doing worse. But if they want to continue using this account, at least they care to some degree.
- If they want to kept themselves not being banned while they can't say they are the banned users, the reasons they do something might be more obfuscated. But with contexts those might be obviously stupid.
- If they wanted to obey the rules, so that they may become harmless, it's more likely they will left. And if they don't, so they are still harmful, they don't care much about registering again.
There can be cases that you want a more strict IP and proxy ban. But if you don't, basically it's the other users' inconvenience not able to recognize the bad user, your trouble to maintain and explain the rules having some unreasonable edge cases, and there aren't really many things to lose for themselves, unless they are valuable at the beginning, in which case you should have more options.
A permanent ban might be a lazy way clearing their score or other users' subscription if applicable, or stating your official opinion when that user is well known. And in some cases it is used only for those, instead of disallowing the users themselves to come back. If there are no such problems, I suggest using temporary ban even if you want to get rid of them forever, but just ban them longer.