Anybody who is a musician - at least at the level of regular and enthusiastic amateur - will believe that musicians are nicer people than normal people. This is something that, in my experience, goes beyond the normal peer-group association - "the crowd of people I have something in common with". In "The Seven Basic Plots", in passing, Christopher Booker suggests why this might be the case.
A fully rounded human being will be developed in all four areas - physical, mental, emotional and spiritual. To perform music well requires development in all those areas. Physical in the sense of the dexterity and strength required to use an instrument; mental because formal knowledge is required to "do" music; emotional and spiritual because music is designed to evoke an emotional and frequently spiritual response, and to do this requires that the performer is in tune with those aspects of the music.
It is possible to perform music without being in touch with all four areas - but there is a perceptible difference between musicians who "get it" and people who don't.
So good musicians will have developed in all four areas that are required to make a mature human being. They are likely to really be nicer people - something which they had hitherto only suspected.