adj. 25B6; adjective
gratuitous violence : UNJUSTIFIED, uncalled for, unwarranted, unprovoked, undue; indefensible, unjustifiable; needless, unnecessary, inessential, unmerited, groundless, senseless, wanton, indiscriminate; excessive, immoderate, inordinate, inappropriate.
they offer gratuitous advice : FREE, gratis, complimentary, voluntary, unpaid; free of charge, for nothing; Law pro bono (publico); informal for free, on the house; Brit. informal buckshee.
necessary, paid.