It bothers me because it's kind of like playing God. Yes, in the short term, trying to promote one team over another may benefit you and help you win the race. But who's to say other teams aren't just as deserving as you to get the money? By doing whatever it takes to get ahead, you are implicitly saying that you are more deserving than everybody else. (I'm not talking about working hard at the challenges. I mean ruthless stuff like passing along answers, which I consider cheating.)
What if Ethan and Jenna had won? Perhaps you are right that Ethan would have donated most of the money to his charity. What if the showgirls had won? Perhaps the single mother could have really used that money. By choosing a contestant(s) to help, you are also saying that they are more worthy, and even worse, that some contestants (like the Cowboys) aren't. It just feels wrong no matter how you put it.