Let's say an old lady takes 1,000 dollars out of the bank and you hit her over the head with a bat and steal the money and get away with no witnesses. You just got 1,000 bucks! Wouldn't you be happy?
Me personally? No. Because I'd be thinking about the lady I hurt. Partly wanted to get that stated so you cannot sidetrack with a "see? You DON'T have any morals", and partly because it comes into play later on this post.
The "problem of morality" can tend to be as big as the "problem of evil" for believers. In the absence of an objective morality, why IS something moral, and something else not? Most people say "it is wrong to thump people and take their cash", some say "it is right to thump people and take their cash".
In the OT, of course - and admittedly throughout history - it is okay to thump people and take their cash/children as slaves depending on who the people are
. Which is why very few civilisations - and why Yahweh himself - have not expressed an objective morality, but merely a subjective one. Yep, even god, because his morality is a person preference of what HE thinks is right for HIM, but which he would not want to happen to him.
Take your example of "thump someone and take their stuff away". Terrible thing to do, right? Except.....didn't Yahweh do just that in the flood? He demonstrates the biggest problem with damn near all subjective moralities - that they are not reciprocal.
Back to your example again. The thief there clearly thinks that "thump and steal" is fine. But would he think that "thump and steal" was still fine if two minutes later someone with a bigger stick walloped HIM and took the money? Willing to bet he would not, precisely because his morality is subjective, a one-way morality. Its why all theistic moralities ultimately fail, demonstrating themselves to be significantly flawed.
Morality - to me - has to flow both ways. If it is okay for me to thump and steal, it must be just as okay for me to be thumped and robbed. But if that were the agreed morality, the human race would never have developed past a big strong guy sitting in a cave: one generation only, because he wouldn't want his offspring to grow up and thump him.
So the reciprocal morality has also to be one that follows the Golden Rule - to treat others in the way you would want to be treated in their place. Yes, Jesus said it….a few hundred years after the Chinese first expressed it, but hey, no points lost for unoriginality! Shame Yahweh's original morality didn't have those sentiments, but he's only the supreme being after all, can't expect him to get things right first time round.
And such a morality - to treat others the way you would want to be treated - is about as objective as it can get. Because it allows for everyone to be treated fairly and equally no matter what their circumstance. You get no benefit from being richer or bigger or faster because the morality is bidirectional.
THAT is the morality of the atheist. Superior to the morality of the theist because it applies to everyone, across the board.