For more than half a century Americans have been conditioned to think blondes are better looking. It's been a pretty good marketing plan I suppose, from TV to adds to Barbie. Blonde hair, blue eyes. There are lots of studies on this and its impact on girls of color, and it impacts white girls as well; there are so many white girls who become blonde just to conform to this mindset, get more attention, etc.
Personally I'm not into blondes. It's not that I dismiss them automatically, but I prefer darker hair. Brunettes are great and should have nothing to be ashamed of.