anti-nuptialist
a person philosophically opposed to marriage, including the wedding itself and associated ceremonial formalities (e.g. the engagement), as well as the legal principles and/or moral suppositions on which this sociocultural convention is based
Tom hated weddings. He was an anti-nuptialist who found the notions of monogamy and commitment implied by matrimony to be socially contrived, arbitrary, and meaningless. Artificial barriers to individual freedom.