As new Sporting Kansas City player Brad Evans would say, Seattle and Kansas City aren’t rivals. That still doesn’t stop both teams, or at least both team’s fans, from not liking each other. I know a lot of people from Washington and specifically Seattle. They are good people. The people who comment on the Sounders on the internet are probably a different group (though most teams most vocal fans online — outside of this awesome community — are often insufferable).
In the classical sense, these teams probably aren’t rivals. Seattle has a series of late, KC heartbreaking, goals that often steal points away.