Shambles said something very interesting, shortly before the George Martin debate began:

Perhaps the term should be reserved for those of us who are prepared to sacrifice the lives of all those who ever get close to them - in the selfish belief that their own life and work are all that matters? Being thought to be a genius - seems to be taken by some as permission or an excuse - to be a complete shit.

I'd take it a step further and observe that some artists can be so obsessed, so taken over, so driven, by their own "genius" or "muse" or "ambition" or whatever, that they wind up sacrificing their own happiness and normality on the altar of their music ~ not just the "lives of all those who ever get close to them."

Based on my brief and long-ago friendship with someone who would eventually gain a measure of recognition as an outstanding songwriter, I can attest that certain people who may appear to be "complete shits" or "difficult" personalities are often harder on themselves than they are on anyone else.

While it's easy to be critical of these "geniuses" for their difficult personalities (while being envious of their accomplishments and success), it might be more appropriate to sympathize with them, even perhaps pity them, for how very difficult they make life for themselves.