Think about it a bit, you may not agree it is right but you know that it is what happens
What you say is indeed biological history and in some eras it was vital that survival be assured through traditional lines and ideologies of the culture. For a very long time mankind survived plagues, disasters, famines and other issues ...by its tenacious grip and ability to reproduce in large numbers. However for the last hundred years or more, modern man has not had the same vulnerabilities which has allowed us the opportunity to reach past the basic survival mentality into a bit more of an enlighten realm. Now the most dangerous enemy to mankind outside of nature is ourselves ... break the chains of oppression we have laid upon each other in the name of survival is the hardest task yet.
I think that at this point in an overpopulated, resource strapped and poisoned world ... condeming love in the name of survival is outdated and irrelevant.