Again, you're assuming that I don't enjoy just smashing the monsters for the fun of it, or that I enjoy the game less the more items I have.
If I have a number of items that will let me make a powerful fire-focused build, but am missing a single key item, how is it game breaking if I trade for that item? Only RNG is keeping me from having the item, and I may have found an item of equal power that I don't plan to use so why not trade? Your goal may be to get more stuff, but mine may be to get the stuff that allows me to play more, but in a certain way.
Interesting view.
I guess it just depends how its done really. the AH is broken because of how accessible items are to people who have nothing. you dont have to earn anything in the game to be successful. if you can prevent that than why not have it.