So late this week I was laughing at Darwinists, and before that I was laughing at atheists trying to express moral outrage. I'm gonna keep chuckling at the latter, embodied by Larry Clapp from CFI, today.
If you define something as "good" because God commands it, then it's arbitrary
Well, 'arbitrary' is sorta right. God has been and forever will be the same. So since He's always been this way, from eternity "ago", it kind of drains the meaning of arbitrary from the term. He is the only objective standard that I've encountered, and you certainly haven't presented one. God commands what is in accord with His nature, not out of some standard extraneous to Him.
Without Him, everyone is a morality of one, and can change their morality at will. THAT'S arbitrary.
But again and again (and again and again and again ...) he insisted on having reasons, which everyone took great delight in shooting down.
But again, you don't have a good reason to say "if you don't have a good reason and can't be consistent with your stated reasons, you should change your approach". Maybe he believes that it's moral and proper to act consistently inconsistently with his stated reasons. You have no access to that, and you can't tell him he's wrong. You're stuck, in a morass. The next time you encounter a pædophile in the middle of raping a child, all you can consistently do is say "I don't like that" and then infringe on his personal morality and rights by trying to stop him. When you do that, you're acting as if you were a Christian. And then you wonder why I scoff at atheism.
by definition, no atheist can be good, not even theoretically.
Now you're changing the topic. This has never been about atheisTs. It's been about your worldview.
Now let me tell you a story, similar to what you told me:
Long ago, men looked around and they saw that eating ice cream indiscriminately led to gaining weight, which they didn't like. They said "don't do that". They saw that eating broccoli led to lower weight, which they liked. They said "do that". They found that doing some things led to stuff they liked and other things led to stuff they didn't like. They encouraged the former and discouraged the latter. Somewhere along the way, they said "This isn't just me saying this, it's the gods saying this! You should obey!" Holy writ, and our "moral sense", is just (ha!) thousands of years of condensed good (and sometimes not so good) sense. But at its core it's just people talking to people, and people agreeing on certain things. Agreement. Between people. That is all.
Anyway, this is completely inadequate. You've begged the question (again) by using the word "good sense". You are unable to differentiate between current Western society, Nazi Germany, and my scenario. In fact, in my scenario, the exact same thing happened as you described, only what led to order and what the society liked was actually stealing little girls from other tribes, raping them, and killing them, leaving their bodies to rot in the jungle. So by your own logic, that's totally fine. Good luck with that.