What Blizz is doing has a good paralell in discussions about drug laws. It is called "Harm Reduction". The idea is, instead of crafting laws based on some moral position and ignoring the harmful effects of the laws, you aim to find a solution that results in the least amount of harm.
Blizz probably doesn't like the idea of items being bought and sold for RM. They've made rules against it in the past. But the result of those rules was a proliferation of 3rd party sites that sold, spammed, and scammed. By introducing the RMAH, they've decided that the harm done by the 3rd party sites was greater than the harm done by introducing RM to the game.
You can disagree with this decision, but you should at least discuss it on the terms that Blizz used to make the decision. They probably would have preferred not to have to do it. I don't think that profitting from it was their primary motivation, or they would have sold items themselves. Many will disagree about that too though:)
I think this also may be a test run for their next MMO.