Devils Advocate

"In common parlance, the term devil's advocate describes someone who, given a certain point of view, takes a position he or she does not necessarily agree with (or simply an alternative position from the accepted norm), for the sake of debate or to explore the thought further. Despite being ancient, this idiomatic expression is one most popular present-day English idioms used to express the concept of arguing against something without actually being committed to the contrary view. " Wikipedia