Addressing theists.

The accusation comes to light often enough that Atheists are immoral - even less moral than other religions that aren’t yours - because they don’t have a divinely inspired - or even a fixed - moral code.  In order to refute this, without actually defining the content of my moral code, I’ll now lead you down a quick logical pathway.

I will assume for the sake of argument that your religious text is divinely inspired.  It contains a moral code.

There are many other religious text - not divinely inspired, as per the assumption, but written by humankind - that also contain moral codes.  They may be inferior, for lack of divine inspiration, but they are serviceable for those that follow them.

These other religions are still around, sometimes for thousands of years.  So they must at least be serviceable enough to prevent societal collapse.

At this point, we can agree that it is possible for humans to write a moral code without divine inspiration that is at least sufficiently servicable to prevent societal collapse for societies following it.  This is exactly what the an atheist moral code would be.

So, no.  Atheists aren’t by definition immoral.  Sinful, by your standards, surely, but in no way immoral.