Part of it is this idealistic adherence to "materialism" that rationalizes existing oppression with Marxist rhetoric. Gay sex doesn't produce offspring, so gay sex must be unnatural and worthy of oppression, and since we see the liberal bourgeois culture being more accepting of queer phenomena, then it must be a bourgeois degeneration against the very real materialism that says sex is always between a man and a woman because science.
As Lenin said, it's an infantile disorder.