If I'm thinking about this objectively, then what's wrong with Chargers fans being happy with their season...I think a realistic fan would be hopeful that the team win the game, but not terribly optomistic because, quite frankly, the Patriots are just a better team.
I actually do liken it to the Pats in 2001-2002, for no other reason than the fact that no one is giving the Chargers a chance in this game. And as a realistic Patriots fan leading up to the Super Bowl, I was hopeful the team would win but worried because the Rams were the better team (and that year, quite honestly, the Rams had more talent on the field, they just had a terrible game plan).
I think it's actually worse to be an arrogant Patriots fan leading up to this game. Yeah, the Patriots are the better team--some would say by a large margin, especially with a hobbled LdT, Gates and Rivers--but the better team doesn't always win the game. I would rather be the type of fan that can admit that while they have more talent, anything can happen on game day. Do I think the Pats will win the game? Absolutely. Am I going to talk as though it's a foregone conclusion? No friggin way.