Saying that a religion is invalid because it borrows from older mythology is certainly a bizarre argument. Not to mention a useless one. I mean, most people know that Christianity and Islam believe the stories of the Torah’s Jewish prophets and built off them or that the Romans took from the Greeks. In fact some this "evidence" was forged by historical revisionists; I know Gerald Massey, who claimed Jesus was a copy of Horus, has largely been discredited by Egyptologists for this very reason. If you know very little about mostly extinct pagan mythologies, which I’m sure a lot of these guys wouldn’t bother researching anyway because it’s not science, I’m sure saying that Jesus and Horus both rose guys from the dead is enough to sway them, while also ignoring that the latter guy has a falcon head and jacked off into his foe’s salads as revenge for being raped… actually I’m starting to wish the Jews did steal from the Egyptians now…