The atmosphere was electric at the start of the game. The stadium was going nuts. The fans gave the team every advantage they could ask for. But when you sit there in near freezing temperature and watch them completely drop the ball against the stinking Cowboys with an extra week to prepare, the fans have the right to be pissed off.
It's a football city. They sell out the stadium when the team is good or bad. Phillies (baseball) can't fill half the stadium when they're bad. Fans don't boo there because every other sport is a distant second to football here.
Booing is a natural expression of anger and discontent. The moment Eagles fans stop booing is the moment they've stopped caring about the team.
And screw Peter King. What the heck does he know about Eagles fans?