Or, homosexual unions don't meet the definition of marriage, and therefore aren't protected to begin with.
They don't meet with the BIBLICAL definition of being wed.
What most people don't seem to understand is that the civil institution of marriage - which is in fact protected under the Constitution and 14th Amendment thereto - does not require any religious involvement at all.
A religious marriage, however, in order to be recognized legally,
does require civil involvement.
Now, there's "Common Law" marriage, which doesn't require civil involvement, but that only exists in 15 states (and the District of Columbia), but even some of those have limitations.
Alabama, Colorado, District of Columbia, Iowa, Kansas, Montana, New Hampshire, Rhode Island, South Carolina, Texas & Utah all still have Common Law marriage that can take effect today. So if you want to get married without having to enter into a civil ceremony and get a marriage license, you'll have to move to one of those states.
In Georgia, Idaho, Ohio, and Pennsylvania Common Law Marriage exists provided it took effect prior to certain dates (the earliest being prior to 1991 and the latest being prior to September of 2003. Which means these are out, because you'll need a civil ceremony to get married in these states today.
And in New Hampshire it exists only for the purposes of inheritance (THAT must be interesting when there's squabbling families).
But "Common Law Marriage" aside, your assertion that same-sex unions don't qualify as "marriage" is simply wrong.
Times have changed, and so have societal norms. It's just the old hangers-on that haven't caught up with the reality of a modern world.