The question is, where to draw the line.Someone could argue why to ban the 5 post newbie over plagiarism, because he could be potentially useful to the forum in the future.
I compare the forum rules to like an agreement of a contract - when I sign a contract, I also must adhere the contract terms, otherwise I have to deal with the consequences.
It doesn't matter whether I've read the agreement / forum rules or not.
And the second question is what to do with people who are banned because of the same reason?
Banned because of one-two non-quoted posts posted 5 years ago. although he later proved himself to be a useful member. They would be collateral harm.