You're missing a few pieces that contribute to the decay of society:
- No they don't build harems, but they are more likely to wait before settling down with a long term partner.
Also, perhaps it's the circles I've run in, but monogomy is far less dominant than it was in the past, and serial dating is far more common, especially when you start looking at some folks interpretations of 'empowerment'. I'm using airquotes here because I'm thinking of someone who would literally always be 'getting over' her last relationship with her current one, but would be checking OKCupid and POF because they were starting to have doubts about the current one.
There's a question of how much psychological damage online dating scene does to how one deals with interpersonal relationships. Most of the 'serial' daters I know get more and more bitter with every failed date, and post more and more vitrol on social media about the opposite gender.
There's also the issue that Dating profiles really often remove so much of the important part of a relationship; getting to know someone, which is a good test of communication.