I was talking to a friend last night as we were watching the NBA Finals and both rooting for the Mavericks. He wondered whether it was right for us to be rooting for a Dallas team given our hatred of the Cowboys? I thought about it a bit and I really couldn't see why not/?
Philadelphia has no built in sports rivalry with the city of Dallas. We're wired to generally root against all New York, DC or Boston teams, but as far as Dallas goes, the only team we pay any attention to is the Cowboys.
Further, who even has any problems with fans in Dallas? I certainly don't like Dallas Cowboys fans, but of all the ones I've met in my life (and it's been many), not one has been from Dallas. Literally not one. Many have never even been there. So all the bandwagon Cowboys fans that we're so familiar with and dislike so much, they share nothing in common with the good people in Dallas rooting for their hometown Mavs (and Cowboys).
So good for you Mavs, good for you Dallas, good for you Dirk! I think basically the entire country was rooting for that team and they delivered.