The video I was talking about:

As for Book - I knew the about the theory that he was some sort of Alliance higher-up at one point. What I find hard to swallow is his quick rise through the ranks because of his especially brutal beatings and such. I just don't think that would fly in any military construct - such behavior would get you psycho-analyzed and ultimately expelled, unless it's a really rotten army. Of course the Alliance is eeeevil and all, but it's not the Star Trek mirror universe where dudes casually stab each other to advance their careers.

Secondly, I doubt that any torturer - spy or otherwise - could switch back to a coherent peaceful preacher identity that smoothly. That's just too extreme a shift for me, seeing how Book supposedly spent years beating up people for a living. That's gotta traumatize you deeply.

But, as said, could be that the graphic novels explain everything I just brought up and I am just way off.