Oh Gawd "I have sinned in my mind". The idea of clean thoughts goes back to far before Aristotle talked about them. The problem is that the human mind doesn't work that way. All it does is open you up to being black mailed by someone saying that you are failing to be perfect. So much evil has come from Plato's quest for perfection. Perfection is a chimera. Engineers have learned that perfection doesn't exist and is the enemy of good enough. Biology doesn't work towards perfection, only good enough. Only humans would be silly enough to be interested in perfection.