To my mind the piece is interesting but not because we need a word such as deepity. We don’t because we have far more well-known words such as slogan. What we gain by exploring the word deepity is to remind ourselves of misleading slogan structures. Hughes gives a good example -
On one reading, this claim is undeniable. Legality is a concept that applies to actions, not people. People can be male or female, introverted or extroverted, blind or sighted; but they cannot be legal or illegal. Like the claims, “no act of kindness is red” and “no prime number is lethargic,” the claim, “no human being is illegal,” is simply a category error.
The term “illegal immigrant” is similarly misleading. It’s not the person that is illegal (whatever that could mean) but the act of moving across a border without following certain procedures. Since the claim “no human being is illegal” is neither true nor false, it literally cannot be denied—that is, you can no more argue that “some human beings are illegal” than you can argue that “some prime numbers are lethargic”—and because the claim is undeniable (in the literal sense), it can sound plausible, and even obvious.
But the second reading of this deepity asserts something extremely controversial: everyone should be able to go anywhere on Earth with no legal or procedural barriers; every border should be fully permeable; strangers should be able to occupy your property—after all, no human being is illegal, and strangers are still human beings when they’re on your property. Needless to say, even advocates of open borders would not endorse this view in full. But if the view were ethically correct, then it would have profound implications for property law, the existence of nation-states, and the very concept of personal space.
The whole piece is well worth reading, but we cannot know if placard wavers actually believe their crudely painted slogans or if they simply see them as a means to an end. Probably both, but in any event dismissing them as slogans isn’t going to make them go away. Dismissing them as deepities is even less likely to achieve that. So we do the analysis, use our own language, ratchet up the contempt and the world goes on as before.
This issue also highlights another, in that we cannot speak rationally with everyone because not everyone wishes to be rational, especially if they would have to analyse their own deepities. So we talk with those who listen and the deepity-mongers know that and make use of it. They always have and as far as we can tell they always will.