Sherlock is equipped to see the worst in people. To weasel out every last inch of their hypocrisy. He had wanted to understand, and so he'd taught himself to see, but in doing so had only distanced himself further from that particular goal. Other people are, by and large, obscure to him. All he does know is that every last thing they do and every last idea they have is meant to serve themselves, even -- especially -- when they're not supposed to.

That most of them aren't worth investment is obvious, and the idea that those that are become that way out of simple genetic proximity is laughable.

"How? I was only born to them; it hardly means anything at all." Perfectly arbitrary, once instinct ends and the reality of human complexity sinks in.

"It doesn't matter. Supposed to, people say that, but I hardly see the point. Doesn't stop me choosing." Which, clearly, he already has done; that's the point. What is this current living arrangement if not something better than family?