The problem with that is that a basic rationality issue is to ask one's self what would make you change your mind. And in fact that's a pretty useful technique. It is useful to check if something is actually someone's true rejection, but that's a distinct from blanket assumptions of disbelief. Frankly, this also worries me, because I try to be clear what would actually convince me when I'm having a disagreement with someone, and your attitude if it became widespread would make that actively unproductive. It might make more sense to instead look carefully at when people say that sort of thing and see if they have any history of actually changing their positions when confronted with evidence or not.