Some say that if there is no morality—or no God—then all is permitted.
All is not permitted. You cannot sprout wings to save a child falling off a cliff. You are not permitted to take your life right now simply because you feel like it. Reality imposes limits. Life could still continue, even with widespread abortion, euthanasia, gender changes, and so on.
“All is permitted” actually means all is morally permissible. So, all you get is another—albeit distorted—morality.
The faiths all teach that conscience has the final say. Catholicism says that there is no excuse for having a badly informed conscience, but if that is all you have then you must never violate it.
If everybody had such a conscience, then moral law would not be a law at all. Imagine a state where murder is banned under penalty of life in prison. People murder. They go to court. They all get off on the grounds that they must have lost their minds. See then that there is no real ban at all. It is just words.
And if all is permitted, you are permitted to act as if you think your morality comes from God. If you expect or ask others to take your word that you are sincere, you are admitting that, instead of being strong and meaningful, morality is built on a foundation of sand. Coherence is simply not possible.
And what does "permitted" mean? If morality is just a “Don’t,” and there is no penalty, then why take it more seriously than someone telling you not to eat a jam doughnut? The “Don’t” is just a word without enforcement. The penalty is what truly forbids in a sense.
If morality is real, we exaggerate its importance. In doing that, we paradoxically can be called immoral!