I don't really see the issue...
Either you duped before, which means you got something out of it while it lasted. But you can't say you didn't realise that it wasn't something PD intended, and as such they might put a stop to it at some point.
Or you didn't, which means you were either against it and are now glad they stopped it (better late then never), or you just didn't care... so you still don't.
the argument "but it's devaluated cars and blablabla" isn't really valid. It's not like an an MMO where items are the only goal in the game. People were never meant to get so many cars so fast, but it doesn't change
your game that
they did.
Cheating is a problem in competitive multiplayer-games because it ruins the competitive element. The only competitive multiplayer element in this game is racing. Yes, someone might now own lots of fast cars... but they can only race one at a time, and getting a few fast cars to compete is not really hard without cheating either. The X2010? it's ridiculous anyway, if someone uses that to beat your "normal" car, it's "cheating" whichever way he got it...
Of course, if you see "collecting cars" as a competitive game as well, then maybe you have a point in saying duping was a problem... but seriously, who cares which cars someone else has?
It's like owning a Lambo in real life, payed for with hard-earned cash, and complaining someone else bought one with lottery money... Who cares? Does it ruin the pleasure of owning a Lambo? I.e., is
your garage worth less to you because someone else has a better one without having worked for it?
If that's the case, it's all just about Epeen... and if so, I'd be happy for them to lift the restriction again, 'cause Epeen is nonsense
edit: for the record, I do think they should have prevented duping from the start. Not just by technically preventing it, but also by making the game so much fun to play that you wouldn't feel the need to