I wonder what Aizen's motives are for his actions. If we look at Tousen's past and that he has a strong belief in Justice I can only conclude one of two things either
a) Aizen tricked Tousen
b) That Aizen has good motives for his evil acts
I think that it is b because MOST evil people still usually have good reasons for thier actions and they do say that "The road to hell is paved with good intentions, that being said what the h**l could Aizen's motives be?!?!