Well, there is also a deep study of Scripture and its relationships in history that can have that effect, too. For instance, my turning point was when I discovered Mithraism had a virgin birth of its savior and his death to redeem mankind 200 years before Christ. At that point I realized that Paul had taken the teachings of an otherwise decent Jewish rabbi and turned them into some messianic bastardization of a number of Mideastern religions.
So where did Paul go wrong? His God lives. The god of Mithraism is dead. Believe in the one you want.