I think designating a group of teams to make them mpay estra or be avoided in trading hurts what we're all trying to get: the most liquidity for every team.
I think that good teams generally pay a little more in trades because they're more motivated to get that last piece or two of the puzzle while bottom teams aren't going to launch themselves to the top with any one deal. While people talk about the strong fleecing the weak I don't think that happens much. Most trades are fair at the time, and some (like ken's example) become decidedly one-sided later. That's life.