Standing up to cheer on the defense during a big 3rd & 1, 4th & 1, or goalline stand is perfectly acceptable. Rising out of your seat instinctively to celebrate a big play, be it a touchdown, sack, fumble recovery, long pass, etc. is perfectly acceptable.
Standing just to stand is flatout rude. I've had season tickets since the late 80s and have sat in same general area since then (M5, now 312). I can never recall a single game in which everyone stood the whole time.
There were prolonged instances of standing (the Denver game in '90 when we scored three TDs in 75 seconds) but never did anyone stand for the whole game.
I get your point that it's a football game, but that doesn't give you an excuse to obstruct other people's view on 2nd & 8 with 10 minutes left in the second quarter. You have to be reasonable. If people are bringing their kids, and they can't see because you're the only a-hole who insists on standing, that's just wrong dude.
Actually, for years I sat next to an older couple who never stood even when they scored simply because their knees couldn't take it, especially in the cold. So they sat and watched the game and cheered on the Bills. Or is that not okay?