It looks a bit harsh and cruel to permanently ban an account for spamming, plagiarism, or whatever the (similar) reason is. It's like a lifetime prison! Even if the thief is caught stealing, it doesn't give him a lifetime imprisonment, instead he's freed after 2, 3 or 5 years. Why can't we apply the same rule here? Most stupid people won't understand anything without a ban (no matter how many warnings they are given). However, going for a lifetime ban for this still looks very harsh.
We have a disproportionately high number of thieves here, though. And it's likely that many of them would re-offend shortly after being allowed back. Some might argue, with the punishment as harsh as it is, they should really pay more attention to the rules and not do it to begin with. Plus, the fact that many of them are now resorting to word-substitutes means they absolutely know what they are doing is wrong. They're taking deliberate actions to avoid getting caught. Then they claim they didn't know about the rule. Don't fall for it. Enough people have been made an example of, but some people are still doing it. The opportunity is there for people to learn from the mistakes of others, but they aren't. That's on them.