Why was Hitler so against homosexuals?

Answer 1

While the National Socialist government of Germany held a special animus against Jews (murdering about 6 million of them), homosexual people were a close second. Between homosexuals, communists and "Gypsy" or "Roma" people, there were probably another 6 million deaths.

Answer 2

It was a mixture of reasons. They were not able to carry out his master plan. Sure, he willingly accepted their help in setting things up, but once things started rolling, he had little use for them. They just could not produce all the blonde-haired, blue-eyed people he was so fond of. Why did he think Aryans were so superior? Did he find Aryan men to be attractive? That brings us to another point.

Then there is what was probably the main issue. He was most likely gay too. History has it that he put some of his best right-hand men to death. He probably did certain things with them, and he may have feared extortion. Dead people cannot extort others or use someone's orientation to manipulate them, so this could have been his motives in having them put to death. He wanted to project a particular image of himself and his country, and gayness didn't fit into it. Just like some historians speculate that he was part Jewish and hated Jews in part because of that, his view of gay people was likely similar. He couldn't accept that in himself.