They're the nation's football team, have been since 6.2.58. Then we've got 29.5.85 on our collective conscience. When they take a shit, it smells of roses; if we plant a rose garden, it smells of shit.
They've also got conveniently short memories. For example, their first two home games in 1971/72 were played at Anfield and the Victoria Ground because they'd been chucking knives into the away end at OT the season before. Google "man utd home game anfield guardian" for the report.
Then when they kicked off in Europe, in St Etienne, in 77, even Anglea Rippon got her knickers in a twist - for a youtube vid google "man utd v st etienne 1977".
I guess they get away with it because they can - even the decision in the Suarez / Evra case shows that and the consequential stream of abuse that our number 7 gets whenever and where ever he plays. FFS even the Hearts fans were at it.