I think the way to go about it is to encourage people to support the team the way you do, rather than criticising them for supporting the team in their way.
I agree, the way some have gone about it isn't constructive.
It's hard to do when you're being bombarded with negativity from such people, but the solution is to smile back at them and show them how much more fun you're having than them, rather than to turn and snarl back at them.