I think things like Tweeter glitches aren't that bad, since they're really just for fun and derping around.
Duping, on the other hand, is ruining the economy, causing items to lose their value and players who have low amounts of money to be subject to inflation as the prices constantly rise, when dupers can just clone their money to buy whatever. On top of that, duping is banned from the forum, if I'm correct...
I'm not "against" either, especially since I do tweeter glitches just to have some fun every now and then. And I've met some really nice dupers who've loaned me money so I can buy something quickly and then give them money back, so I'm still at least making the money at one point or another, and some have given me things that were cancelled in WW and CF that they obtained before they were removed, and then duped a bit before giving it away to less-rich people.
But yeah. I think that duping is just a way that people can play their game; I'd get bored pretty fast having whatever I want whenever I wanted it, but hey, some people like that. And as for tweeter glitches, those don't help you advance in the game, but just let you walk in the river a bit for fun.