The first definition seems obvious—indisputable, even—because our dignity as human beings really is closely tied to our autonomy, our ability to choose freely, without coercion. If our will is so weak, or so impaired, that it’s useless to us, we lack a certain kind of dignity. Human beings are meant to be free—at least free to choose our own response to what happens to us.
The second definition seems obvious for a different reason—because we don’t feel dignified in the midst of something ugly or embarrassing, messy or humiliating. Some of the most profound and characteristically human experiences--birth and death, for instance—are neither pretty nor fit for public viewing nor neat and tidy. It feels as if they lack dignity. Very few deaths could rise to the level of "dignity" in this sense.
So why pseudo-obvious? Here are some examples to illustrate the inadequacy of both meanings.
In honor of our recent commemoration of Veterans Day, let’s consider a military example. Suppose a soldier is killed by the surprise attack of a suicide bomber. He didn’t see it coming. It was out of his control. He was at the mercy of the terrorist.
His death meets none of the criteria of the first definition, but do we really want to say it lacks dignity?
Or take another case: a soldier knowingly enters a life-threatening situation to save his comrade. He warns his friend in time, and his friend escapes, but he himself is tortured and then killed.
His death is ugly and messy. But lacking in dignity? No.
A similar misunderstanding is at work when it comes to conception and birth. "Reproduction with dignity" hasn't caught on, but the obsession with maximum control over timing, gender, and technological options certainly has.
The thirst for absolute dominion would make some sense if we were all-knowing and all-wise. Maybe the delusion that we are, or that knowledge and wisdom don't matter, is behind that horrifying story of the woman who "paid $50,000 to have a girl."
And even if we could control conception and birth, then what? I understand all too well the temptation to try to micromanage your children indefinitely, but I understand that it is a temptation, not an ideal. As Simcha Fisher says here,
When we realize how little control we have over our children's lives [not just their gender at birth, but their whole subsequent trajectories], we have the choice of either pretending we can control them (which will ruin their lives and ours), or we can let the burden of control be lifted from us, and realize that it's our job to try as hard as we can--not necessarily our job to succeed.
The most dignified choices may not look dignified at all. We can use reason and free will to space pregnancies or postpone them, to distinguish between ordinary and extraordinary means of caring for a patient, between preserving life and prolonging dying.
But if we define dignity so narrowly that only God could meet our conditions, we're on the wrong track.