I think it matters very much. If your morality is not derived from the creator, I would argue that your morality is likely to be highly flawed.
The key here though is that in a free society we are going to approach issues with different moralities depending on where we obtain our morality (religions or philosophy) and how well we have thought through that morality or how well we have listened.
The question then becomes which morals should we legislate. Are there a subset of morals that are important to us all, such as murder, theft, assault, rape, that we agree should be legislated.
The harder question is are there morals that should not be legislated. Start with sins that are not overtly a violation of another's rights. Such as lust.
Can lust be legislated? There are things that you can legislate. You can outlaw pornography. And American society agrees that there are a poorly defined set of obscene things that should not be part of the public square.
You could probably argue that Islamic burka's are an attempt to legislate preventative measures to lust. I would argue burka's cover's God's beautiful creation and is morally wrong.
There is a point, where man's attempt to create model societies through legislation rather than through changes of the heart, goes horribly wrong. Burka's are an example. Does that invalidate all attempts at legislating society. Certainly not.
He does have a lousy position to defend.