Let me make sure I understand what you’re saying here. “Evil” is often used, in a religious sense, as a disembodied force that causes people to do bad things. I agree that in a natural world, there isn’t this kind of evil.
But more commonly, “evil” is just a word people use to refer to actions that are on the very bad end of our morality scale. And it’s common for many theists to say that without God, there is no right or wrong, no morality. That seems to be what you’re talking about, so I want to make sure.
Of course there isn’t any absolute morality. The very idea of morality is that it’s fundamentally an opinion. I think it’s wrong to torture babies, and you do too, and so does every other sane person, but that doesn’t make it anything more than an opinion that’s shared by everyone - it’s not absolute.
The theist who argues for absolute morality will then say that if it’s just an opinion, then all opinions are equally valid and you can’t say that it’s immoral to torture babies. This is wrong - I can say that in my opinion it’s immoral to torture babies, and so does pretty much everyone else.
Since morality is an opinion, I don’t even know what an “absolute morality” would even mean. Even if there is a God, that wouldn’t change the situation. He would have his opinion on morality, you have yours, and I have mine. Just because God has the power to torture me forever doesn’t somehow make his opinion absolute. It’s still his opinion.