I'm curious why a question like this is even asked. How in any way would his belief if it's a choice to be gay (which its obviously not) affect his ability to run the country. I wish we could actually talk about the issues for once.
Answered your own question. As you said, it's obviously not a choice. So if he answers an obvious question wrong, he's obviously a dullard and not fit to be president.
I strongly disagree, just because he doesn't know the facts to answer a random question like this does not disqualify him for the presidency. He has a great list of accomplishments as Governor of Wisconsin that surely make him fit to be president. The people that say this disqualifies him from the presidency weren't voting for him anyway, luckily I don't think the majority of people would change a vote based on something as silly as this comment.
No. You had it right the first time when you said the answer was obvious. It is obvious. Only an idiot would answer anything other than "no, it's not a choice". Furthermore, it's not a "random" question. Gay rights was/is one of the biggest issues in American politics, the field in which he works. Walker supported a state constitutional amendment to ban gay marriage and was the defendant in a court case to overturn that amendment. If he really took such a strong stance on gay rights and never thought about whether homosexuality is a choice or not, if the question was really "random" to him, again, it proves he is a gigantic idiot and specifically that he doesn't think through policies before he commits to them. Very extremely relevant to his ability to be president.
