From a logical standpoint, not at all.
From a social standpoint, it often does persuade people towards the pro. However, that is a known fallacy. It is a standard tactic in persuasion.
From the movie "Thank You For Smoking":
Joey Naylor: ...but you didn't prove that vanilla was the best...
Nick Naylor: I didn't have to. I proved that you're wrong, and if you're wrong I'm right.
