The Oxford English Dictionary defines marriage as:
The formal union of a man and a woman, typically as recognized by law, by which they become husband and wife.
It seems to be the term “marriage” which is the problem in this contentious debate. But why the fuss? Surely it is still possible to coin a new, suitable word such as uniteage for instance? This word contains unity, unite, a bit of the word “marriage”, uni for one sex etc. What more is necessary in a mere word? Surely it is the act that is important and not the word.
It is time to let go!
N.B. Where laws now exist where the word, perhaps with some qualification, is inscribed in the law it can easily be changed and exist in its own right.