I'm not even sure what this means. Anakin isn't capable of rational thought? This is just nonsense. Anakin is plenty capable of rational thought and demonstrates this many times throughout the prequels, he just decides not to use it when he doesn't want to. Anakin was just under a lot of stress and self-imposed pressure and handled it very poorly. It wasn't insanity, it wasn't mental illness, it was just the very poor decisions of a very flawed person. That's about as nice as I can say it.