It's an intriguing hypothesis, to be sure. My understanding is that most scholars reject it (the hypothesis being that religion began from the worship of extraterrestrials who acted like gods on Earth). So that rejection is either sound and fair, or it's part of a coverup and a conspiracy to hide the truth. This feeds into the bad sort of conspiracy theories (self-reinforcing delusions). If the hypothesis holds up, we should be able to see what's wrong with the scholarly criticisms of Sitchin's views.