I know where you're coming from...
The simple fact is that Commanders fans are supposed to hate the Cowboys and Cowboys fans are supposed to hate the Commanders. Only a few of those involved in this rivalry can actually remember why, though. Most of us, including my 27 year-old self, are born into the rivalry.
When I stop to think about it, I have no real reason for hating the Dallas team or its fans. In fact I don't hate Cowboys fans in general; of course there are always the select few that I dislike, but that goes for any large group of individuals. As far as my feelings for the Dallas team, I always root for them to lose, no matter who they're playing. Next come the Eagles, Giants, Broncos...I don't hate any teams (I don't like to hate anything), but I do care for certain clubs less than others.
Some people take sports rivalries too far, see soccer brawls in Europe and an above poster that wants to attack Commanders fans on sight as if seeing red like a bull. It's just a game, and we're just spectators.