It's because blondes are seen as a privileged class (sure they're blonde, but they are dumb, too, so they don't have it all)-- it's reassuring for people who feel inferior-- and that blondes are seen as unattainable/out of our league and believing them dumb makes them more approachable and more attainable. It's pretty reasonable.
Joe DiMaggio, I mean really, by any measuring stick -not a looker.
Arthur Miller wasn't as ugly as Joe and is the best looking of this bunch, but that's not saying much.
JFK, I don't know, maybe I am just too much of a dyed in the wool Republican, but he never did anything for me.
Then his brother, please, it's lunch time and I don't want to make anyone sick so I will just say he always looked like Abe Lincoln to me. Abe may have been a popular president, but I doubt he was popular with the ladies.