There is no objective basis for morals.
Oh, yeah. I forgot. Good rebuttal.Is that objectively true? If so, then your humanist morals are based on an objective truth. Your objective truth is that there is no objective truth. So the basis of your morals is that it's basis does not exist. Therefore, the superiority of humanist morals lies in them being not superior, so they are superior.
OK - there's a god..