See the interview with OKCupid’s president on NPR.
There is a valid point to be made, I think, that pretty much all businesses “experiment” or “research” to determine what is effective. And in the case of dating sites, I can see an argument that they need to test the value of their matching alogrithms. But then why not make that clearer in the terms of service and privacy policies? And – as we considered after Facebook published its research that had been conducted without opt-in consent – at what point does “research” require opt-in consent? If you may manipulate lonely people’s hopes and feelings of romance through your “research,” should that require consent – or at least notice? If people, as a result of your research manipulations, may go out and spend money on a date or have a bad encounter because of your intentional manipulations, do you have any duty to them?