I think dating sites had genuine members some years ago, until, (like some have said), married men and men in relationships found it could be used as a knocking shop. As did some women.
I used dating sites for about two years and met some bizarre characters. Most of these men claimed to be seeking longterm relationships, but the reality was they enjoyed meeting new women every week and often for sex.
Unfortunately, dating sites are now full of misfits, who are incapable of having an honest, monogamous relationship. I met my partner through a friend, I think that can be the most successful method of introduction.