There is a king, and he has people working for him who make sure people do what he wants them to do and not what he doesnt want them to do, and they do this by punishing those who do things the king doesn't like or who don't do things the king wants them to do.
However, some people get away with it because the law enforcers don't catch them, so what does the king do? If he can't keep the people obedient to his rules, his kingdom will not last much longer!
Well, that's where religion comes in! It makes people obey the rules by saying there is a super king that's bigger than the king who is just a man, and if they break the rules then the super king will punish them after they die. So it all works out.
Religion also solves many other problems as well, and I won't get I to those purposes here but let's just include one of them that going to war is a whole lot easier when dying in battle or childbirth is a way to ensure you get to live in paradise forever.
Now, if you interrogate a religious person about why they are religious, you will eventually get to them saying that they want to go to heaven and do not want to go to hell, because heaven feels good and hell feels bad. Makes sense that every religion in history has had something like this, believers who follow the rules get rewarded with something good, and unbelievers who break the rules get punished with something bad.
So the real reason people are religious is that they are ruled by the pursuit of good feelings and avoidance of bad feelings. God is moral because he is the one who decides which of the two you will get after you are dead.
All morality boils down to this by the way, and all you have to do to expose this is ask them why enough times to get there. It doesn't matter if their ethics comes from religion or philosophy. Its all "because I would make me/you feel better if X were to occur, and it would make me/you feel worse if Y were to happen instead".
Both answers of the eupythro dilemma ends at the same place, by the way, if things are good because god says they are, then the basis for that is that god can make people feel better or worse, and if things are said by god because they are good, then the basis for good that god is referring is still more good feels and less bad feels vs more bad feels vs less good feels.
Accepting that an individuals feelings are their ultimate source of morals means not that they should impulsively pursue what makes them feel more good and less bad in the moment, because one must take into account the ratio of good to bad feels overall in the course of their futures.
The best thing to do is make a set of rules that when adhered to strictly, would cause the individual to trend towards having more good feelings and less bad feelings. And never make exceptions since these rules must become habits and making an exception even in the case where it is unambiguously beneficial to the individual for them to do so will cause them to make a habit of breaking their habits as exceptions naturally widen and the basis for making exceptions becomes looser and looser.
But past that we can ask why certain things make us feel good and certain other things make us feel bad. The answer is genes and from there we have the principles of biological evolution.
Things that make us feel good do so because the genes that produce good feels in response to them were better at replicating themselves, and things that make us feel bad make us feel bad because of the same reasons.
So the ultimate ethics is that whatever we do that makes our genes replicate more and not less is good, and whatever makes our genes replicate less and not more is bad.
And many people would stop there, as we can see groups like white supremacists who are the best fit for this sort of philosophy in my humble opinion.
However, there is a level beyond this which is looking to the purpose of evolution itself, because there is a clear pattern established and its heading somewhere, or at least its trending towards some ultimate ends.
That's the species which could expand beyond the solar system and survive the death of their home world's native sun. What do we know about such a creature? They would be the most technologically advanced, able to survive optimally in any environment by either adapting themselves to it, or adapting it to themselves. Clothing and houses both come to mind.
So the greatest purpose of life is that, and if ethics is anything, its having a purpose to serve that serves as the basis for making rules that one should live by. The purpose establishes the concepts of a positive state and a negative one, so that the rules which are set have a means of being judged and assessed.
That's all I have to say on the subject. And I'll add this: the problem with most athiests is that their standard for morality is how well liked they are by others. Like the Christians they spent the millennium decade arguing against, they are just as much ruled by fear and guilt and shame. Both Christianity and the new atheist skeptical rationalist whatever community were built on the same instincts. No wonder why they turned out to be equally pathetic.