A gay person existing doesn’t actually literally harm anyone though. A homphobe shouting slurs at a gay person, excluding them from vital social, economic or whatever activity or beating them up does very concretely harm someone. It’s not that difficult.
You can get a cat for who it is more beneficial to stay inside. For example cats who are scared and skittish or cats who are fiv positive. The former should stay inside for their own safety and the latter for other cats’ safety. And they too deserve a home :)