The problem isn't the BYU losing to Utah. That sucks, but absolutely worth it for cancer cure (my 5 year old son is currently battling cancer).
The issue is that I don't trust the devil to hold up his end. Plus I feel like making a deal with the devil isn't good for my immortal soul. I probably wouldn't make a deal with him for a cancer cure in exchange for BYU winning for the next 30 years either. Just because I don't generally like the idea of being in league with the devil