“We ought not argue.” This can only be asserted if you argue, as part of an argument. So it contradicts itself. If it is true, you ought not say it and you ought not to argue at all. By arguing, you demonstrate your disbelief of this proposition. Your actions implicitly affirm that you disbelieve the proposition that we ought not argue. (Or do you? Perhaps you affirm “we ought not argue, but I don’t obey the rules.”) 

Am I entitled to claim that “We ought not argue” is false?

Does that mean you believe the logical negation of it? What’s that? You ought to argue? You may argue? You ought to be able to argue? You are at liberty to argue, if you are able? You have a right to argue, and others have a duty not to interfere? Must we conclude that the concept is incoherent?