“If there is no God, everything is permitted.” This is considered wisdom by your fellow citizens but it shows us the form of gaslighting by defining a false binary, which is how the classic misdirection works among humans.
If there is no God, the question of “permitted” rests with human beings and our individual selves. What do we permit ourselves to do? What do we tolerate in others?
Even more, sane people calculate their actions by consequences, so the question of “permitted” is secondary to “what will achieve the results needed,” a question which itself links to the question of what sorts of long-term effects are present.
But to escape the misdirect, we have to look instead at how we choose actions. We are not interested in a binary yes/no on methods, but a goal… and within that, we know ourselves and our quality by the choics we make, which means that those who aspire to more than the mundane will seek better choices.
In short, the question of permission is irrelevant to those who can think, and those who cannot need to be oppressed by some kind of system that enforces relatively non-destructive behavior, or at least removes egregious cases of the destructive.
You can see how they fool you. If the only thing regulating your behavior is fear of Hell, then without God you will be in trouble, but this only applies to people who are broken in the first place. Sane people regulate their own behavior in order to achieve results.
They also tend not to aspire to more than they need, simply because this is a burden without actual gain. People want normal happy lives, not control over the known world, if they are relatively sane.
Anything is permissible. You are known by what you do. Depending on your genetics, this may have more or less constructive, creative, and renewing behavior in it. But most of all, you will be known by what you do by yourself. And this we fear more than God, because time moves only one direction, and we must live with our memories.