Oh, yes, very good point! If Sherlock’s lived a life of mainly solitude and rejection, it makes sense that he would want to separate himself from feeling badly about that as well as make sure others don’t see him as “poor Sherlock, can’t make any friends”. Convincing others he’s a sociopath would be a better alternative as they’d be forced to think he’s alone because he wants to be (which may be largely true, but not completely; at the very least, genius needs an audience).
As for the ‘maybe himself’ bit… Sherlock does seem to want to separate himself from anything emotional, especially going by the fireplace scene in Hounds. “I’ve always been able to keep myself distant. Divorce myself from…feelings.” We know from the original stories that his only friend in university was Victor Trevor and I can’t imagine he had many friends before and after that (Seb Wilkes certainly wasn’t a friend). It would be much easier to deal with that loneliness if he could convince himself that he just doesn’t care about any sort of relationship.
Not to mention, it would serve him an advantage as a detective. We’ve seen that he’s often quietly affected by the deaths of innocent victims; not necessarily on a typical “hero” level, but enough so that it would be important for him to push emotional responses away in order to effectively do his job. Secondly, he needs to rid himself of emotional biases anyway in order to make sure he’s working only with facts and logic. Otherwise he won’t be nearly as successful.
And all this works without him necessarily having to be autistic, as well, so I quite like that.