More Kant? Yes, more Kant. You know you love it.
Kant ends the Transcendental Analytic section of the Critique of Pure Reason with a discussion of, literally, nothing:
The object of a concept that contradicts itself is nothing because the concept is nothing; it is impossible (nihil negativum) - as, say, a two-sided rectilinear figure.That's merely one nothing among four, but then it's the only one relevant for this post. "Square circle" is another good example of this sort of nothing. Because the thing supposedly described cannot exist in reality, no object corresponds to it; further, because the words comprising the nothing are meaningless when so combined, the nothing is not actually a concept at all. No possible object, no concept - this is as non-existent as a thing can get.
Contrast something like "purple unicorn." This object does not exist in reality; that is, the phrase does not apply to any real existence. But the concept at least exists, because a coherent set of qualities is described by that phrase. "Purple unicorn" is a concept that describes a possible object. That we will likely never find an actual object corresponding to that concept is not important. When you read the phrase, you have a concept of what is written.
So, "gay marriage"? This is a meaningless combination of two independently significant words. The combination annuls itself. It expresses nothing.
So, should gays be allowed to join in civil unions with precisely the same benefits as married couples? Oh, I don't know; that issue seems to have disappeared. But perhaps we could discuss it more usefully without making up nonsense phrases and empty nothings.