Defining success of civilization is an important feature for understanding what builds and what decays a society and its culture. To be blunt and honest, anyone can agree that without a man and a woman there would be no society, let alone culture or civilization. While it is absolutely true that every culture has had homosexuality, often it marks the declining period of said society, such as the Graeco-Romans, for example. Note that the pharaonic dynasties of Egypt were, too, often corrupted families of hedonists. Take the eunuchs of ancient China, who were forced into service in the harems, as this is an example of how certain aspects of homosexuality originates from slavery.
So, what builds and transforms a society, and what decays it? Well, as a Baha'i, I look at the history of civilization as inspired. A successful civilization has revolutionary arts, advanced sciences and mathematics, inspired literature, and most importantly, cultural propriety. And while homosexuals have been known to contribute to civilization in various capacities, I personally argue that they cannot progress it--merely on the basis that there is not a single culture who honors same-sex relationships and there is not a single society that has not fallen when cultural propriety falters.:slap: