I've heard many reasons.....Steinbrenner's spending is bad for baseball...etc etc etc
I happen to disagree with that though. You said yourself how the Yankees playing the Nats brought a "playoff" atmosphere (or something like that I think)
They fill up stadiums across the country even if it is just so people can go and boo them.
Steinbrenner spends a fortune but I believe attendance at Yankee Stadium will go over the 4 million mark again.
As a fan, I would rather see the owner of my team spend money to improve the team as opposed to what the KC Royals owner does.
Another reason many fans hate the Yankees is because they are from NY. It's easy to hate NYers and anything about NY I guess. I don't quite understand that either....maybe because I've lived here all my life.