BS! To the extent that "culture" is valueless and amoral, I would agree ... they have disproptionately contributed in that area. But to the extent that roads, infrastructure, buildings, music, medicine, communications, government, and just about anything else that lays the framework for a culture and society, gays have contributed nothing outside of the roughly 2% that they comprise of the general population. And when you consider the healthcare costs, the degragation of morality and values, and the double-speak politically-correct thought-crime nonsense that they are pushing, I would posit that they are net-negative contributors to a healthy culture.
I take it that you don't visit too many museums then. While it's hard to be sure, Leonardo Da Vinci is considered by many to have been a homosexual. He was certainly accused of this during his lifetime. He contributed a bit to our learning and culture.