Is there room for Objective Morality in an Atheistic Worldview?

Having recently been through a conversation with some atheists who insist that moral values are objective, but that God is not required to ground them, this article has been bumped to the top of the to-do list.
These atheists were convinced that objective moral values are just a fact of reality, and that the concepts of 'goodness' and 'sentient well-being' were identical. They seemed to think that either moral values are weaved into the fabric of space somehow, or that sentient beings just have the intrinsic value of being good, that is to say, sentient beings, i.e. humans, are valuable and good in themselves without any need for further explanation.

That to me is nonsense. The idea that humans are basically good, but get things wrong a lot of the time is common belief. History tells a different story. From gladiator games to the Stanford prison experiment, we've seen that apparently good people can be barbaric given the chance. That's not to say all people would devolve into savagery at any opportunity, but it very much undercuts the idea that humans at core are fundamentally good.
I tend to think it's more like the Native American parable: inside each of us there are two wolves fighting, one represents good, one represents evil. Which will win the battle? The one that we feed.

But atheists tend to go further. They will say that other things or behaviours are intrinsically good too. If you found a starving child, giving up your lunch and feeding it would be the good thing to do for its own sake. While I agree that in that case that would be the good thing to do, I don't think it can be claimed that the only details you need are a starving child and some food to offer. There are a number of questions that can be asked.

The Weakness of the Worldview of Atheism

Atheists tend to describe atheism as the most reasonable and rational position to hold. But then again I'm sure most people believe that of whatever worldview they hold to, so I wouldn't hold that against them.

The short explanation is that they believe science is on their side and the evidence for theism is wanting. I will here clarify that by 'atheist' and 'atheism' I refer to the views that "God does not exist" or "God probably does not exist".
This doesn't speak to the agnostic non-theist who is on the fence.

But consider this worldview. Does it stand up? Can it stand up? Maybe. But it is on the thinnest of ice.