Prolibertas -

But what we ought to do about it has got to be decided on the basis of what reduces suffering best, surely.

Why do we want to reduce suffering?

Paley -

It's interesting that Euthyphro's Dilemma could also be asked of the atheist as well. It something good because you say it is good? If the atheist says yes then goodness is relative which no one is ready to accept or live by. If the atheist says no, then he is affirming objective morals values without a foundation which is irrational. This is quite a dilemma for the atheist.

Something is good because, roughly speaking, we collectively decide it's good. Is that relativist? Relativist to humans, yes.

Take a sentient species of alien. Food is scarce on their world at certain times, and they are very fertile. Therefore, at some point in their past evolution took them down a certain path. They would eat some of their children to survive. They still do, given the potential for famine. If they don't, the species would die out. Are they wrong to do this?

But the second part of your alleged dilemma is strange as well. Let's imagine a conversation -

Moral realist: I believe objective moral facts exist.
Paley: Ah, but you must explain where they come from. You can't, therefore it's irrational unless you think they come from god.
Moral realist: Why should I? If we don't know where they come from, we don't know where they come from. We can't just give up and say god did it.
Paley: But you can't explain, can you?
Moral realist: So what? And I can explain. I'm a non-naturalist. I can give a definition of 'good' that reduces to other qualities about the world that are much less controversial. Given my position, I don't need to invoke god at all!

What's your response?