There seem to be two issues here that get mixed up together. One is whether there's any reason why the State should have any objections to people in same sex partnerships being able to have the same recognised arrangements as in mixed partnerships. The other is whether the term marriage is appropriate in same sex partnerships.

When people say they are in favour of civil partnerships, but are against these being called marriages, that's surely just arguing linguistics.   A bit like "what is folk" - getting all het up over a mere label that doesn't really matter a great deal.