Some say writing is a lonely activity and therefore writers are loners.
Writers are hungry for the world around them. They devour human drama, desperation, pain, madness, crimes, despair... In their hunger they are insatiable and thus - often difficult to put up with. But, I would not say - loners. Solitary, perhaps. Solitude as a choice of lifestyle, or rather - a necessity.
Just because someone craves solitude does not mean one is a loner. Even when the number of friends and colleagues dwindles, one is not necessarily lonely. True loneliness starts when one does not want to see friends, when one does not want to make new friends, and when one does not want to share thoughts or experiences with friends. Even so - it is loneliness by choice, driven by compulsion, but as such it leads to freedom. No?