Though less of an actual anti-marriage-equality ad and more of an intentional parody created by Brandon Muller of NonRandomNonSense, "The Ultimate Anti-Gay Marriage Ad" nonetheless manages to get across the anti-marriage-equality camp's grievances against same-sex marriage better than most real anti-marriage-equality ads.
Of course, in doing so, it also manages to make it abundantly clear that opponents of same-sex marriage have no real grievances besides the ones that are ripe for parody.
[H/T: Good As You]