I don't know Brian personally so I have no idea how he's wired. I couldn't possibly make an adjudication about his sanity or lack there of.
Given that a person is not to the extreme of being a sociopath, no matter what the upbringing or experiences, I still think that having personal integrity or any number of exhibited personality traits is a choice. Still that choice may be more difficult for some than for others and some traits may seem almost impossible to change. Even so, I still believe that even if those traits are ingrained in us, there is always still choice. If that were not the case, we could never change.
In the case of a sociopath, I agree. If a person simply has no conscience and completely lacks empathy as a disorder, well, that person is damned.
I don't think Brian is insane, or a sociopath -- well, maybe a touch of the latter -- but, from his posts, which I found very strange at the times, I can envision him being so caught up in his own turmoil (mixed with a self-image that includes considerable grandeur), that it became incapable for him to reason or feel for the situation of others. So, he became blinded by the situation he found himself drawn into.
I can think of times this happened to me, when it really hurt someone I loved, so caught up was I in my own confusion and feelings.
You've got to also remember that Brian NEVER exhibited the devotion to the critical cause, so to speak, or even cared to work out his own case in public, admitting any kind of real guilt -- not in a "pulled it in" way but any complicity whatsoever. Like he never said, "I really let my ego get carried away there, when at Flag they started making me believe I was this person who could help so many people," or "Boy, was I stupid!" Of course, sometimes, as we know, those kind of realizations take years for ex-members to deal with.
For Brian, karmic balance may have meant getting his money back, because CoS had deceived and manipulated him -- which they did. At some point, he decided this would be his release, and something that would also allow him to exit the scene.
One thing I've noticed is that in a lot of cases, the more a person put into CoS, in years, their youth, their childhood, belief, trust, the pain they suffered -- the more they are willing to devote to fighting them when they get out, IF THEY ARE MOVED BY THE PLIGHT OF OTHERS. Brian was a wealthy dabbler -- a spiritual traveler. He didn't end up cleaning toilets for them, or wrestling with guilt about regging so many friends and family into it.
It couldn't have been easy realizing that he was historic in epic dupedom either. That isn't how HE viewed himself, certainly. He wasn't like ex-members, like Luis for example, who may rationalize that Scientology helped him become successful in life and business -- even if it did these other things. Brian was already rich and accomplished by most anyone's standards, when he started as a Scientologist. Even Jenna could rationalize that at least she met Dallas through this journey, and she didn't have to deal with the idea of "getting herself into it."
It's possible he took the strategy of claiming some benefits from it, and hanging around the indies (on Marty's blog anyway) because it would help his case for getting his money back. He saw that that helped Debbie Cook. If Debbie Cook had said, "I don't believe in this shit anymore," would that have helped her case? When he saw that strategy wasn't working and this was just dragging on, he began Plan B -- just get out. Get the Miscavige cult freaks off his case.