I agree with your post, BH. IMO, two reasons to veto a trade:
(1) Collussion - people getting together to screw the league.
(2) Unconscionable - trade is so bad that the league can't let it stand.
There is a fine line between an unconscionable trade and one you just don't agree with or don't like. IMO, the trade has to be pretty bad to invalidate it. I think E. Smith for LT2 has to be invalidated because it is unconscionable, regardless of whether collussion can be proved. Your other example of Lewis for Chris Brown I think has to stand, absent some proof of collussion, because there is at least some basis for trading away Jam Lew, i.e. his legal situation.