The only response you will have is that banned people will disclose a lot of accounts, with a lot of useless posts, just to have more probability to have a functional account.
It seems to me that this is not a good results.
I think that a better policy would be to give a warn, and - if there is no effect - only then to give a permanent ban.
You know, probably we are too many here, too many useless posts, so we need some moderation, even this is a hard one.
Of course the rule that says that you'll grow in rank by posts number is the main cause of garbage posts.
Btw, I agree that a warn could have better results than a permanent ban.