I made a long post in a topic on the PS3 board about why I don't care but it basically comes down to 3 things
1) Legendary loot offers unique gamelpay mechanics as opposed to simply having good stats like most games in this genre.
2) The loot is very rare and tied to a RNG
3) The best ways to obtain the legendary loot involve repetitive grinding as opposed to simply playing the game. THis combined with the poor drop rates gets frustrating quickly.
So basically I am fine with people duping or Gibbing legit gear because locking of unique gameplay mechanics behind a stingy RNG that requires repetitive grinding to run is not good game design.
There being several different versions of each Legendary is the biggest problem though. Even if you do happen to farm for one and get it, the odds of it being the one you actually wanted are very low. That makes the drop rate feel even that much smaller.
Not to mention that you still have a parts issue as well to deal with. Getting the perfect set of parts for your weapon is futile really when it gets down to it. You to go through all these % drops before getting what you really want:
1. Legendary drop rate for ANY Legendary.
2. Getting the right prefix for that Legendary of the 3 or so options you have for each one.
3. THEN, even though the barrel is brand related on oranges, you still would ahve to hit the luck meter off the charts to get both 1, 2 and the weapon parts mix you want after that.
Most players don't know the difference though and have no idea that #2 and #3 even exist as options for weapons. Once you know about this and have your mind set on the perfect build of a weapon, however the farming doesn't just become "I just want a Legendary to drop". It becomes "I want a Legendary to drop, with this prefix, and these parts". On top of ALL that, you even get hosed sometimes when you beat a Level 50 enemy and they drop a Level 48 version!
http://img.photobucket.com/albums/v643/ripvanwallace/scarlett_johansson_ass.jpg Don't you just want to bite it?
I stopped playing online w/ randoms because I had people joining my games i was hosting demanding dupes from me--who would then continue to message me after I kicked them. So in a sense, duping sort of has hurt my online experience. That said, I'll dupe for friends if we both want the same gun, which isn't very often.
The one thing that I don't like about duping is the sheer amount of LF "trading" threads and topics asking for dupes that clutters up the board.