The big reason for the betting rules are NOT whether or not you’re for or against your team, it’s what happens when you get in debt to people that live on the wrong side of the law. By illegally betting on sports you’re volunteering to be blackmailed. That’s where most of the big point shaving scandals in history come from, not because they bet against their team, but to “work off” debt.
I understand the idea of that, but I think the " people that live on the wrong side of the law" line was crossed a long time ago in many more ways than gambling. In a sense pro sports has become much like Washington DC where some laws are posted as window dressing but no one really concerns themselves about it all that much.