if I say buddha is indeed bishnu's avatar and buddhism is nothing but a branch of hinduism and i totally believe what can you possibly do to change that? How can one argue about something as abstract as faith/belief? one can believe whatever they want evidence in history hints in vedas will not change one's belief because beliefs is something you take to be true without having to prove. I don't believe buddha was god (he himself said it) not do i think he is avatar. As a matter of fact the whole idea of a personal God is beyond my understanding and God coming down to earth to teach us dharma sounds absurd. maybe that is another subject. but no try with all your might but you can't change the reality that hindus will always consider buddha as their avatar and buddhism as part of hinduism.