It irks me that you would rebut this guy with this argument simply because I know that the empiricism strongly leans toward personalities remaining very stable throughout the lifespan, and that changes move together as a population than within-individual. Academics might not have yet built consensus on a general personality theory (Big 5 is more a descriptive research framework than a theory), but there is consensus on personality empiricism.

Surely there is another angle of counter. I don't believe in winning argumentation by any means, especially by scientific disinformation without empirical cause.

Show me someone whose personality has changed without significant personal struggle and I'll show you a lobotomy.

This is a fair point, but why do we as hackers and entrepreneurs place so much importance on what's in a company's "DNA" then? Because right here, you have a pretty damn stark view of the founder's mindset at the genesis of his startup before and as it was taking off. It isn't like he was chastened by external forces along the way or since - ostensibly everything that's happened since has only been positive reinforcement (A billion+ users, 45 billion dollars).

I'm not saying he still feels this way or didn't or couldn't change his thinking and attitude. Common decency would behoove him to and it's reasonable to grant that. I'm happy for him and his new family, but away from all that and his foundation (which sounds very positive), It's hard not to view a lot of what Facebook does with its users through the kind of cavalier attitude embodied in that old chat log. In fact, it helps makes a lot more sense of some of their moves if you do.

Counter evidence with counterevidence; it could be a good assumption. Even if someone's personality is not static, it doesn't mean that the variation is large enough to be significant, either.