oppugner

/əˈpjuːnər/
noun
  1. A person who criticizes, opposes, or attacks something, such as an idea, belief, or system.
    • The senator was a fierce oppugner of the new tax reform, arguing it would hurt the middle class.
    • As an oppugner of censorship, she wrote articles defending free speech.
    • The historian was known as an oppugner of popular myths about the ancient world.