So why can't you make a rebuttal without bringing up something that has nothing to do with the comment.  It just shows you don't have an argument to rebut.  

If you want to talk about the birther movement, then do so.

But I think most people would say that there was nothing to that movement - it wasn't even a movement.  It was just people saying something that was so far fetched that only those who would believe it would never have entertained voting for Obama.