Dear Person-campaigning-against-legalising-same-sex-marriage:
I would assume that, for consistency, if we lived in a country where divorce was illegal you would be campaigning against making it legal, including against the rights of e.g. Jews and Muslims (whose tenets permit divorce) to dissolve their own marriages. Perhaps you would insist on a union between Jews being denoted as a “soluble partnership” so as not to sully the word “marriage”?