I don't think betting against your team makes you any less of a fan.
I bet on Whittingham to score first in the Cardiff home game this season. We were 4-0 in about twenty minutes, and Whittingham looked about as useful as a large tub of nutella on the pitch. I was still happy. I'd rather lose money and win than lose and win money. Winning a bit of money does soften the blow, though.