SImple question. Why do Atheists think that all Religious People are non-scientists? And that the two disciplines are contrary to one another ?

Never said that myself. People always like to bring up the fact that the man who came up with the Big Bang theory was clergy.
The opinion is, that scientist are bound by realistic, provable evidence.religion has to acknowledge the unprovable supernatural, at least as far as the existence of god applies.
Sooner or later, the two are going to come into conflict