There are no ranks that have a religious requirment, such as attendance at church, etc. While the BSA permits and promotes participation in P.R.A.Y.'s religious award program, they are not BSA awards and earning them is not required for any rank. And you are quite right; there is no need to earn any rank to participate in Scouting. I have told more than one Scout, "You don't have to earn Eagle to be a good Scout. I never earned my Eagle, but I think Scouting did me a world of good." This is not necessarily popular with the parents, but it's the truth as I see it.
I agree with your assessment about the parents and Scouting. It's not about the rank, it's more about what the boy learns and becomes while participating.
Cheers!