I have no problem paying a TA for services rendered. If they can find me fares which I cannot do (I typically use them on last minute trips), I feel their services ought to be compensated. Again, they work for me not for the airlines.
The only concern I have is that TAs might steer me to airlines which still give them commissions due to the obvious incentive instead of the airlines with the best fare. If I ever experience this (who knows I probably have), that company will lose my firm's business.
Even though I'm CO metal, I am only a Silver because I have to look for the best fare. If CO isn't competitive, I won't give my business there. This is why I rely on the TA.