Prior to the Viet Nam war, enlisted personel were not allowed to wear civilian clothes on liberty or off base except in certain circumstances, those circumstances being while on leave or if their duties required civilian attire. The reason for this were simple and direct, the lockers on barracks and ships didn't not have enough space alloted for civilian clothes so only uniforms were allowed.
As a direct result of personal attacks by anti war protestors, enlisted personel were allowed to wear civilian clothes when not on duty.
On my way home from Boot Camp in unifrom in 1975 I was assaulted by an "anti war protestor" complete with peace signs patches, bell bottomed jeans, a field jacket, and the sort of body funk that would strip paint, in a Greyhound Bus station in Jacksonville Florida.