There should be no limit on the amount of discussion on PhysicsOverflow, as long as the discussion is primarily about Physics, and not about conspiring about a physicist's integrity, or something as pointless as that.
I see no issue in a question like "What are some reasons to believe that Loop Quantum Gravity is incorrect?" or "What are some ways to falsify String Theory?". Such a discussion should by all means, be on-topic because it gives rise to useful content.
But the discussion can't go on until the topic is not physics any longer. For example, I am against a question that asks "Was Einstein a fraud?" because the discussion is no longer primarily about physics.
If one of the users in the discussion makes a remark about something off-topic, then the discussion is not to be harmed. For example, in a discussion like "What are some ways to falsify String Theory?", if a user makes a comment like "M-theory was a plot by the martians to enslave the world!" (I can't remember where, but I'm sure I've seen this before on some forum), then the comment can be deleted, but the discussion that is on-topic to the question about falsifying string theory can go on, because it is primarily about Physics.