If what one "thinks" is in conflict with reality then their thoughts are not rational. Regardless of ones moral upbringing people are still capable of evil.
You mention "only" actions and consequences. One could easily claim that Christians obey the dictates of G_d not out of a sense of morality but to escape eternal pain in hell. This, if accepted, and I don't, would indicate that there is not a higher morality but simply actions and consequences.
Is an irrational person capable of right and wrong? Of course but likely by mistake.
There is nothing rational about Muslim extremists and there is nothing rational about Nazi's. Bushido, as I understand it, is neither an ideology nor a religion...but regardless I don't know enough about it to determine its rationality.
I disagree with you on the rationality of evil Islamofacists and Nazis and other dictators. It has been entirely rational though out most of history to take what you want by might. The vast majority of evil doers never get their just reward in this world.
Or any world if there is no afterlife.
Everyone is going to leave this existence, so in the mind of atheists, if you do whatever you want and suffer no consequences here, you did no wrong. If you do wrong and no one finds out, you did right because it's right for you.
I find it to be a bizarre concept, but I understand if someone is committed to the idea of no higher authority, they have to come up with something to make it square in their own minds. Bizarre, but understandable.
Peace