How might someone who makes these claims respond to me if I were to point at a cat and say the word "cat" refers to that? I am aware that this is probably a belief that one can't hold consistently, but I'd like to have a better understanding of what "words have no meaning" means. I don't want to try and diagnose Loughner per se (since we don't know a lot about him), but more generally someone who fits the character of the little we know about him--in other words, an abstraction of him. I'd like to have an idea of what philosophy underlies these sorts of claims and how it might lead to his behavior, if it could.
I'll take a shot at answering my own question and see if there are any better answers.
Since words refer to reality, this claim seems be the result of some type of detachment from reality. Maybe this belief is founded in a primacy of consciousness metaphysics, but I think it's more likely the result of some version of social metaphysics. (Maybe those two are closely related.) A passage from Ayn Rand's The Comprachicos seem relevant:
The sentence "The issue, to him, is now metaphysical" is powerful. She points out that this type of person allows others' opinions to be the source and standard of values, and therefore of one's happiness and self-esteem. If one lived in this type of "reality", the primary purpose of words would be to affect and control others. They wouldn't necessarily refer to objects that exist. There is no objective reality, because that changes as others change their minds. Reality is chaos.
He sees no contradiction between his cynical maneuvering and his unalterable fear of the pack: the first is motivated by and reinforces the second. The will of the pack has been internalized: his unaccountable emotions become his proof of its omnipotence.
The issue, to him, is now metaphysical. His subconscious is programmed, his fundamentals are set. By means of the wordless integrations in his brain, the faceless, intangible shape of the pack now stands between him and reality, with the will of the pack as the dominant power. He is “adjusted.” Is this his conscious idea? It is not: he is wholly dominated by his subconscious. Is it a reasoned conviction? It is not: he has not discovered reason.
Also, this would explain his animosity towards others. If one is trapped in a world where the achievement of values is determined by others, we are much more likely to resent them. The more consistently one holds this metaphysics, the less objective reality would seem to exist. And in frustration at being at the mercy of others for achieving one's values, one might even go so far as to attempt to kill those that represent the greatest threat to the inability to achieve values, i.e. those in the highest positions of power. The fact that Loughner's friend places a lot of significance in Gifford's inability to answer Loughner's question suggests there's something to that.