Well yeah, I don't get it. Functionally you can do exactly what you claim to want to do with or without an in game AH of any sort. There is nothing preventing you from farming for your item forever and instead of trading or selling the incidental items you get, you could just destroy it all. It is your choice.
Maybe I need to read between the lines. Is it simply that you suspect the existence of an in game cash AH will cause blizzard to adjust the item drop percentages to make it take 100X as long to farm? I don't think that is even possible, given how the economy of diablo 2 worked (or didn't work, depending on point of view). Trying to get the perfect suffix/prefix combo on the perfect item in diablo 2 was like trying to win lotto, and if you had to do it without ever trading with another player, well good luck to you.
Or is it just that you like the item for item trading rather than trading for a currency in an auction house where everything is equalized? As a buyer, the AH is a huge plus, you can easily see who is willing to sell the item you want at the lowest price and decide to buy or not. Without it, you could easily be taken advantage of or ripped off by a seller who has a fairly common item that you just think is rare or hard to get. I could see why such a seller would be against an AH, as it would make it much harder to rip people off.