Theists can appear superficially successful in such debates, especially if they happen to be ordained priests used to preaching to a congregation. When it comes to public speaking, practice, I imagine, can be an advantage. Comment about the debate appeared on the associated blog, including from Ian Powell, the debating theist. His comment revealed the basic disagreement that I'm attempting to address:
Elsewhere the disagreement often surfaces in the form of a statement or a question asking why an atheist should care about anything, since we are all nothing but chemical reactions and electrical impulses. Atheists will counter this argument saying that since they know this life is all they have, all the more reason to live it to the full rather than simply marking time until going to their (non-existent) heavenly reward. Some go further and question how "truly moral" someone can be if their actions are dictated by fear of divine retribution, rather than by the actual benefit conferred on their fellows. It's a valid riposte, as far as it goes, but it doesn't address the fundamental issue. What the theist is really asking is: "Where is your ultimate authority, if it isn't God?" A Christian, for example, may answer this on behalf of atheists by saying that atheists put themselves in the position of ultimate authority, or that atheists invent an ultimate authority, perhaps by making up an alternative set of "humanist commandments".
...I really am genuinely puzzled that quite a few atheists don’t seem to see the logical rational difficulty (at least) of starting from base reality of energy etc and working step by careful step to an intellectually coherent binding moral "ought" – socially convenient ought- yes , evolutionary helpful ought - yes – but not one that has any ultimate legitimacy.
This misses the point. Christians who ask "Where is your ultimate authority?" frame the question on the basis of their own ultimate authority, namely God, or the Bible as the word of God. If an atheist claims neither of these as the ultimate authority, the theist naturally wants to know what actually is the atheist's ultimate authority.
But there is no ultimate authority. Not God, not scripture, not the Ten Commandments, not the Humanist Manifesto. Nothing. The ultimate authority does not exist. Morality has evolved as a way for humans to survive in social groups, and continues to do so. Now that social groups can be global, morality needs to reflect the aims and wishes of worldwide communities. Rigidly clinging to ancient dogma is, at the very least, inappropriate.