"Atheism is a religion like not collecting stamps is a hobby" -- Penn Jillette
Gods that don't exist can't have sons. These are questions of history, not faith. There may be evidence for the existence of a man of that name, but frankly a lot of the other details of his origins, life and death are implausible and unlikely.
If there was such a person, I'd say it's more likely he was suffering from a mental illness that made him say and do irrational things, perhaps including willingly martyr himself. Certainly not the last case of seriously deluded egotism or making stuff up. L. Ron Hubbard and Joseph Smith have form, here. Given the long history of human culture, societies and mythology in particular, 99% of which is now no longer taken seriously by anyone, it's more likely that gods are inventions of man, not the other way around.