"We know dogs aren't born mooing." At first, it seems like a stupid question. But once you understand the context, you realize it's a very, very stupid question.
But what about people? Are they "born gay"? An interesting question. Many, if not most, people who report themselves as gay seem to feel that way. I have yet to hear anyone finish a sentence with "and that's when I decided to be gay." Kind of telling, isn't it?
But that doesn't exactly answer the question. I'd like to answer the question with a question: Hasn't anyone in focus on the family ever seen a dog fuck another dog in the ass? Dogs only follow their natures - that was the original premise of asking why dogs don't moo. So it seems fair to note that dogs - and many other animals - show us that gay behavior is part of the repetoire of "natural" behavior.
In conclusion: "We know social conservatives aren't born thinking for themselves. But can they learn?"