This NYT story has some relevant insight into the civil union versus marriage debate. It seems that in practice, it isn’t very hard to call civil unions marriages:
Marcie Horowitz and Margaret Maloney of Westfield, partners for 22 years, stood near a display of tiaras and flower girl dresses as they discussed their upcoming ceremony. Ms. Malone noted that no one at the convention hall was referring to the ceremonies as civil unions.
“Everyone’s saying marriage or wedding,” she said.
Now, if they gave exactly the same legal rights and benefits, I can see why it would still be offensive for the official name to be civil union and not marriage. But if they didn’t give the primary right of marriage, and everyone accepted that attempting to have children together would be unethical, I would think that it wouldn’t be offensive at all for the official name to be different. That doesn’t mean people can’t call them marriages, and it seems that everyone does.