Is there any reason to suppose that religions are not scams?
I would think that simple common sense would make it apparent there is no reason at all to suppose this. I don't know how one could possibly look at all of the world's religions throughout history and somehow conclude that they are all scams. One would have to have a very special sort of selective observation to possibly find that even remotely reasonable.
But I'm probably being too generous with my expectations for people's understanding of religion. Ignorance about religions is even worse than people's ignorance about the sciences in my country.