Though I’m sure I’ve fallen into this myself at times, I’ve got to say that I’m usually immediately suspicious any time someone—candidate, interlocutor, whatever—relies on an appeal to “common sense” when trying to persuade me of something. Why? Because “common sense”—whatever that is—is wrong? Not necessarily. I’m suspicious of this kind of tactic because it’s a defense of an argument that has nothing to do with the quality of the argument.
What do I mean by this? Well, when someone says, “This is a good idea, because it’s just common sense,” they’re really using a sly rhetorical device to discourage disagreement by challenging the listener’s intelligence or, maybe, their connection to “common,” everyday, practical wisdom. It almost amounts to loudly shouting about the validity of one’s argument without demonstrating it. “This is self-evident. Why would you disagree? It’s common sense. Everyone should know it.”
The speaker here is implicitly saying that the listener will pay a cost for disagreeing, because denying “common sense” is denying something readily apparent or self-evident. Denying “common sense” thus becomes admitting one’s own supposed intellectual shortcomings (or, maybe, the shortcomings of being over-intellectual, depending on the speaker’s particular ideological bent). If the tactic works, the listener accepts (or refuses to challenge) the argument not because the argument is valid but because the listener doesn’t want to deny or, maybe more importantly, be seen to deny “common sense.”
That’s sad, because the speaker has made acceptance or rejection of the claims a statement not about the argument but about the listener. In that sense, it’s also pretty intellectually dishonest, whether or not the speaker knows he or she is hiding a deficient argument.
Of course, even if the speaker really is appealing to something called common sense when it comes to politics, is there any evidence we’d want to privilege that anyway? I’m not so sure.