Ignorance of the law does not exempt from punishment! Why can’t this be said of an atheist who does not observe the commandments?
I heard that Rabbi Zimmerman wrote in one of his books (I need to look up where) that even a drunk shepherd on a remote mountain would give judgment or have people come to him with complaints. To a certain extent, of course. Because he could use his intelligence and reach the right conclusions (perhaps he meant like our forefather Abraham).