I never saw the point of booing, personally. Yeah, I get upset about the team's play and grumble to myself or complain to the person beside me, but never have I felt the need to yell BOOO as loud as I can. What is the point of that? You think you can motivate the players better than the coach can? Those kids work their asses off every day of the year, overcome injuries of all kinds, and study very hard to cram as much football knowledge as well as academic knowledge into their brains so that they can try to win a game for your amusement.
Give them a break and support the kids even when they're having a rough time. If you have to blow off some steam, go outside and bitch to all the smokers at halftime.