Peace of mind is a very fine thing and , to a certain extent, probably essential to health and happiness of the individual. However, cultivated as an end in itself, as a means of shutting out the distress of other people and ignoring moral imperatives to act, then it takes on a selfish quality which I find peculiarly unattractive.
Then again, you really have to have peace of mind at a reasonably deep level if you are going to be any use to anyone so, like many qualities, it is all a matter of proportion and balance.