Atheists get their morality from the same place believers do: Social consensus and constantly evolving social standards .
The idea that religion is the source of morality, or that it is necessary to produce moral individuals, is one of the big lies propagated on behalf of religion. Religious believers delude themselves that morality comes from their God.
The problem is that The Golden Rule of Jesus is a platitude that provides very little guidance in the real world. OF COURSE we should do unto others as we would have them do unto us, but once you have admitted that, what do you do with it?
I am sure the people who heard Jesus say that found a it was a wonderful idea. They went home and told their wives (who remained in the home and obeyed their husbands) and their slaves (yes, they had slaves). Then the man of the house took a wooden rod and gave a severe beating to his child who had misbehaved (for the bible clearly tells us that we will spoil the child if we spare the rod).
Now flash forward two thousand years. We still agree that we should do unto others as we would have them do unto us. But how many of the above elements would our society consider moral behaviour? What has changed and why?
Take slavery. There is no specific condemnation of slavery in the Bible. Indeed, if you want to make an argument FOR slavery, the Bible will supply enormous support. The Bible even contains instructions on how and when you can sell your own daughter into slavery. So why would 99.9% of people in our society call slavery evil and immoral?
Because our social consensus has changed.
Take the 10 Commandments. Are you seriously going to believe that when God told Moses “Thou shalt not steal” nd “Thou shalt not kill”, it was the first time humanity had an inkling that murder and theft are wrong? The Egypt from which the Hebrews had just left had NO LAWS aginst thses things??? Come on!!!
The Bible actually orders the Israelites to not only observe the sabbaath but to force everyone in their country to do so. But in most westrn democracies, forcing another human being to observe your religious sabbath would be illegal, an a violation of their civil rights.
Where did we get the idea of civil rights? When did we decide we should not burn people as witches?
Most democratic western states were imprisoning homosexuals within living memory. Yet nobody at the time felt they were failing to apply the Golden Rule in doing so. But today, nobody but a few ultra-conservatives would be in favour of jailing gays.
Where in the Bible or religion does it say that insider trading is wrong?
How about cruelty to animals? The Bible does not condemn it and the Golden Rule obviously applies to humans. The British, only a few generations ago thought bear-baiting (in which a chained bear is torn apart by a pack of dogs) was great fun. Frenchmen in past centuries used to set baskets of cats afire at fairs with the full approval of religion. What has changed? Why?
Morality is not and has never been really the product of religion. Society establishes its values. Religion may help a little by scaring people into good behviour with threats of hell-fire, but religion is not the font of morality.
So we all get our morality from the same source. If not, our jails would be filled with atheists and agnostics who, lacking religion, would be incapable of moral behaviour.