Religious principles cannot be manufactured, neither it can be made by speculation. So actually, there cannot be many religions. The rascal theory that "There are as many religious system as I can believe... You believe something, that's all right. I believe something, that's all right. He believes something, that's all right." No. It is not like that. Then everyone will believe like any nonsense thing that becomes religion? No. Religion means dharmam tu saksad bhagavat-pranitam [SB 6.3.19]. Religion means the codes, the laws, given by God. That is religion. Man cannot manufacture.
Lecture on Srimad-Bhagavatam 1.3.19, Los Angeles, September 24, 1972