I'm Catholic. And I am SO sorry.
That really gets the point across powerfully. Unfortunately, I can just see the right-wing types dragging out that old line that "gay people already have the right to marry, they want special rights to marry people of the same sex". *sigh* I guess some people see what they want to see, but that doesn't make SENSE to me.
I hope the ad works, though. I never thought about it quite that way, but you're right - it's completely offensive that gay people have to get everybody else to give them permission to marry the person they love. For most of us it was hard enough just asking the parents!