So we must all be insane

If you're insane you continue to live, if you're sane you die. Ironic, isn't it?
But that's what any religion in the world will tell you. We're here to learn our way towards enlightenment, we're here to clean our soul from sin, we're here because we are prone to evil.
... Could it be that everyone in the world is insane?
Then a second question pops up, which is about forgiving. If you've done something really wrong, does it really matter if you knew at the time that it was wrong? Does ignorance excuse our faults? Is killing because you're commanded to do so, less severe then killing because you can? Is lying because you don't want to hurt someone worst than lying because it's just in your nature?