The criteria for a red card had been met by the reckless manner in which he entered the challenge.
The rest is up to the ref, he can ignore it, give a yellow or give a red. He gave a red, you may consider it to be harsh, but it was ultimately a fair sending off.
As for Rooney (and probably the ref), it may well have looked worse than it was, and in that case - Rooney seeing Kompany try and break Nani's leg in half, but miss - he had every right to shout about it to the referee.
I actually think it's quite sad that Man City are trying to spin the fact they lost into some kind of 'moral victory', it's pathetic.
The funny thing about all this is, wasn't it the same teams involved in the fa cup semi final where Scholes I think it was got sent off for a high foot?
I remember the Manchester City fans being in uproar at the awful tackle at the time. How quickly these things are forgotten.