As far as I can remember there were millions of SA men, they all knew Rohm was gay, and they were his devoted followers. Rohm wasn't purged because he was gay. Rohm was purged because he had millions more potential fighters than every other group of fighters the Nazis controlled combined. His homosexuality was the justification for an overtly politically power grab. It's the propaganda campaign they used to explain to the people why Hitler was turning on his best friend and closest ally. Rohm's street level SA was a threat to the other organs of the Nazi Party, especially Himmler, and represented a massive concentration of power that Hitler did not have absolute control over. And even then, Hitlers other lieutenants apparently had to bully him in to turning on Rohm because apparently they were genuinely friends who like and respected each other.

I could be wrong about all this, but that's the history as I understand it. Much like the designation of Jews is arbitrary, and fascists can turn on any outsider group, the enmity against homosexuality is also arbitrary. Hypermasculine states have had normalized homosexual behaviors since time out of mind without any internal contradictions. If the circumstances of industrial capitalism had arisen under a society with different sexual attitudes than late imperialist Europe they probably would have picked something else as their rallying point to define themselves against.