Sentence:  Just as individuals can opt to continue a marriage, or terminate it, at any point in their married life, likewise a society can, apparently, "opt for"—or against— opposite-sex marriage, same-sex marriage, contract marriage, covenant marriage, polygamous marriage, <WSD>multiamorous</WSD> marriage, or any other socially sanctified ordering of intimate affairs, calling any of that "marriage" if they so wish, and not commit social suicide by so doing. 
Meaning of the word marked with <WSD> tags:  Having many romantic or sexual loves.