IMO, Leary basically said that it's easier to believe in Tom Cruise's aliens than in the Virgin birth, walking on water, the miracle at Cana, etc.
Well... OK - so?
I mean really... in every religion there are "unbelievable" acts that people take on faith... and he compares them and makes that point. The reason people believe in these stories ~isn't~ because theirs seems less miraculous, is it?