If you don't like it, don't buy anything.
People already do it under the table for games such as World of Warcraft, diablo 2, etc. Making it legit is just good business sense.
Edit: you claim to have played diablo 1 & 2. The duping and item sale in those games didn't bother you at all but this does?
No, making it legit is full on embracing the idea, which I've stated is completely contrary to what a fantasy game is all about (IMO, of course). What value is in-game gold going to have now? What percentage of players who find highly desirable items are going to choose game gold over real money, when given that choice? So people actually playing in the game world only (like I would, in this hypothetical scenario) are going to have a significantly reduced experience while using the AH.
When did I say I wasn't bothered by D1 or D2 duping, etc.? I lost interest in D1 shortly after I got all the uber awesome duped gear. Everything was too easy, and I already had the best gear, so there was no longer a reason to play. With Diablo 2, I rarely traded for gear, and usually played solo, though online. Once in a while I would do group games, mostly for leveling up. I stopped playing about 2 years after the game came out, and at that point, the item selling wasn't as rampant as it ended up becoming.
Edit: I'm wondering if you won't be able to drop items on the ground in this game. IIRC, each player will get their own drops from mobs and bosses, so it won't be a click-fest like it used to be (or at least this was the case some time ago). They have also said that you won't need to go to town to sell your unwanted items. This makes me think that it's possible you won't be able to avoid the AH for trading. As in there won't be a way to just trade item for item with another player? Though as I say that, I can't imagine that happening. Of course, I wouldn't have imagined these other things happening either =P