As intelligent beings we know that rape, murder, theft and violence are wrong without the need to have these ideas handed down to us from a supposedly omnipotent, omniscient, omnipresent supernatural being. Blockquote

Yes, we know that now. Not so long ago, rape, murder, theft and violence were not only condoned but also ordered and encouraged by god along with some other atrocious things such as slavery or death by stoning. We as social animals, as an evolving species that developed empathy, love, trust and compassion, realized that those things were not good for our evolution as either a species or a society, so we've ordered them away (wherever possible) by putting laws into place that forbid doing them. And those places where such horrors are still commonplace, we consider barbaric. So I don't think there are objective, immutable morals, at least certainly not handed down by god. Morality is a human creation and as such it evolves alongside humans, and what works today may not work so well tomorrow and we'll need to revise it and change it to adapt it to our vision of society and the world at any given point in time. Not only that, since morals change often depending on the situation (is it moral to kill an assassin that would have taken the lives of 50 people or is killing immoral in every case?) I don't think we need objective moral; we need morals that work, period.

As a side note, I think that Sam Harris's The Moral Landscape is a good read on this topic.