You don't let it pass.   You writ a diary in which you challenge the message of the ad.  You point out who is trying to promote what message for whose benefit and at whose detriment.  That kind of a diary I'd rec and hope to see at the top of the rec list for as long as the ad runs, or longer.

What you shouldn't do is be an ignorant asshole and insist that by helping the lobbyist waste its money advertising here that DK readers, posters and owners are "supporting" the message.

I won't rec this asshole diary.