Hmmm. That is something I have not thought of. Maybe the "damn fool idealistic crusade" Anakin leaves Tatooine to follow Obi-wan on is in fact, a mission to defeat the Emperor.
Suppose at the Beginning of EPIII, we find out in the scroll that in the interim b/w EpII and EpIII, Palpatine has declared himself Emperor and is using his clone Army to enforce his own form of government accross the galaxy. Trying to overthrow a dictatorship and restore a true democracy could definately be called an "idealistic crusade." And to Owen, a young man on a remote planet where the Republic has no influence, trying to restore democracy to some far off republic could easily be seen as "damn fool."
why would i want to eat a 100 dollar bill? besides, it makes sense. Theres too much to tell in EPIII as it is. If the crusade Anakin and Obiwan fight in has to do with Palpatine declaring himself emperor, the story will unfold so much better. As it is, it is a MAJOR plot point of EPIII. If it doesnt happen at the beginning, theres no real conflict worthy of bringing anakin into the war. At the end of EPII, Sidious tells Dooku that everything is going as planned as tens of thousands of clones are boarding troop ships. Obviously they are going to fight Dooku. EPIII is roughly 2 years later, the war against dooku is successful. You cant hold off an army of clones that long. Before EPIII starts, Palpatine will have an army of clones and no one to stand in their way. Obiwan comes to get Anakin from Tatooine to fight against Palpatine. They most likely enlist the help of Dooku who has since come to his senses and realizes that he must help the Jedi in order to keep Palpatine from destroying him.