Your understanding of their reasoning comes from a fundamental assumption that your choice is the correct choice for every person. They willingly made the wrong decision, therefore they must have been manipulated into doing so.
Many people do just become religious without outside influence. On a large scale, every society will create its own version of religion without fail. Clearly, they have something to gain psychologically by doing so.
While religious indoctrination obviously exists and obviously is a problem, it doesn’t discount the actual benefits that religion seems to have, and by extension the reasoning with which some people become religious.
We all do.
When I said “start”, it was in reference to the process of changing your religious identity, not your life as a whole.