Nevertheless, the idea that morality depends on God is still just as popular as ever, and it is even held by some otherwise intelligent people, one of whom is William Lane Craig, who, in the following debate against philosopher Shelly Kagan, articulates better than most this seemingly obvious but ultimately self-defeating position.
The interesting thing to notice in this debate is how easily Kagan sweeps the floor with Craig's black and white thinking, appeals to consequences, arguments from personal incredulity, and other fallacious presuppositions. It's an intellectual bloodbath well worth watching...
For a different take on this issue, you can also watch William Lane Craig debate philosopher Louise Antony. Craig's arguments are, if I remember correctly, exactly the same, but Antony's take is different from Kagan's, and brings in a different way to counter Craig's wild assertions.