I've heard this a lot but I really don't think it's true. It certainly doesn't explain the numbers. Even gen Xers weren't being dragged to church by their parents at anywhere near the rates the boomers were. As a millenial, growing up, I intellectually knew some families went to church, but I only met a handful of kids for whom that was a reality. None of those kids grew up to be anti-theists.

The fall of Christianity and the generation it was most noticable in are conflated, but you have to look a few generations back to find the actual beginning. Millenial anti-theism has its own mythology about the evils of Christianity, but none of them ever actually went to church to begin with, let alone experienced any kind of Christian "oppression" like they claimed to feel.