In many countries/states, civil unions are the norm for gay people, and have been for some time.
However, the current debate from gay people seems to be that they want to re-use the "marriage" label, which has traditionally been for between a man and a woman.
I'm not saying it's right simply because it's tradition - but trying to argue that it has been anything but between a man and a woman for thousands of years is just historical revisionism.
So yes, you can try to argue that, we should redefine marriage to include between any two people who want it.
However, to claim that they're somehow being "oppressed" because we don't simply let them win their argument is just silly.
If this was really about them wanting benefits, then the civil union would achieve that.