Re: Significance of Zaraki's comment on Gin and Tousen in Chapter 65?
It's a reasonable assertion given that these two captains have joined the enemy.
We might assume Zaraki is very good at analysis in his own way, given he was able to best tousen's bankai where others would almost certainly fall, and without using the full extent of his power.
If we assume that aizen brought them into the fold by the promise of greater power, then it's entirely probable. Gin seems to have learned to survive in the world by obtaining power and trying to claw his way to the top. Tousen sees that he cannot effectively bring about his draconian form of justice without substantial power.
We also know that aizen as the master manipulator might simply be just using these two to further his own goals, much in the same way he appears to be using the hollows and the arrancar. The motives behind gin and tousen might be made more transparent when we understand aizen's true goals, given they have supported these ideals based upon their own views of the world, much like any revolution of sorts.