That is because most of the people who plagiarise do not know it is against forum law. They act like it is the regular classroom cheating where students copy each other and submit without getting caught for malpractice. But this place is different and people pay heavily for that when caught in the net.
In the first place people shouldn't be stealing others work intentionally as that's a dishonest act and anyone caught should be punished, it doesn't matter which part of the world you're from and how things are been done over there but again I don't don't support the permanent banning of people on their first offends. A better punishment could be to disconnection the monetary privileges that the forum offers for some period of time and see how active the user still is. We have seen this happened before and some users who got this punishment has turned out to be better contributors of the forum.
The immediate banning only encourages the creation of alts by this users and it's unlikely they put much effort into that accounts since they have it at the back of their mind that they can be banned any moment their secret gets exposed. Anybody that gets banned and that account wasn't a useless account, I think they deserve a second chances. Take always their privileges but don't make them stay away from the forum. Personally I don't know what I'll do with myself if a mistakes gets made over here. Some just see this as a forum but to us this is more than that and it isn't just about the forum privilege but the connection and wonderful people this place has connected me with both home and abroad. If the users own up to his mistakes, he should be pardoned.