The only evidence I've seen to counter this (very common) critique is the disturbing practice of 'chadfishing'. If you make a profile and put a picture of a hot guy, you will be flooded with female interest.

Make a profile with a really hot guy pic and see what happens. You'll find there are way more women on those sites than you thought. Or better yet, don't do that, but look into the people who have. They tend to be crazy people (who invented 'chadfishing'), but their results are fascinating.