There is an argument going on among well-intentioned and more or less knowledgeable bioethicists about the question of whether there is much use in deploying the concept of 'human dignity' in resolving conflicts about normative questions in the field. Here is a good critical take on the issue.
Typically the issue of dignity is wheeled in by opposing sides when they don't like the stance held by the other side, and they have no good arguments left to defend their own take on the matter. Here's a few examples: voluntary euthanasia and physician assisted suicide. There's opponents of physician assisted suicide and voluntary euthanasia who claim that such means to end a persons life are not dignified. Certainly the Roman Catholic Church thinks so. If you know anything at all about this debate, you will know that 'Death with Dignity' is also the battle-cry deployed by voluntary euthanasia groups. The same concept is used without blushing by groups for diametrically opposed means. That's odd indeed.
Up to this point I talked about the concept of dignity as if there was one. Of course, if neither the euthanasia folks nor the anti-euthanasia folks are able to demonstrate that the other side is wrong in their use of the concept of dignity, quite possibly there is something wrong with the concept, or, more to the point, quite possibly there's no concept.
Is voluntary euthanasia the exception pointing to a small problem with the idea of 'dignity', or is there actually more evidence that 'dignity' might just be a vacuous motherhood-and-apple pie thing suitable for and against anything and nothing. Well, in fact, there's plenty of other examples. IVF and artificial insemination (to go the the other end of our lives) are in the same boat as euthanasia. Christians routinely argue (well, claim) that our dignity is violated if we use such means of modern reproduction, allegedly because it's against our nature to do so. Of course, they don't mean a matter-of-fact type nature, they mean their normative understanding of what our nature should be like. It is well known that people who require access to such means of reproduction think their their dignity as rational agents is violated if the state or others prevents them from exercising such a choice (gays and lesbians come to mind, for instance). Both sides deploy the idea of 'dignity' to advance their diametrically opposing stances! Odd indeed.
Pornography is another, and my last example. There is no consensus at all about the question of whether someone violates his her or dignity (and that of others) by watching or participating in the production of pornographic material.
The German enlightenment philosopher Immanuel Kant initially understood respect for someone's dignity really as respect for a rational, autonomous agent. In that sense, dignity is kind of a short for respect for autonomous persons. That probably is a sensible thing. All other things being equal, we should be respectful of at least the self-regarding actions autonomous beings wish to undertake. May be that is what we should be saying, however. Of course, since then religious folks and invariably the UN have stepped in with a deluge of dignity here and dignity there declarations and statements that resulted into dignity being reduced to a campaign tool for everything and nothing at all. Christianity, for instance, quickly removed the Kantian criteria of reason and rationality and agitated for embryos' dignity, and human rights related claims derived from those. In case of doubt the supposedly necessary respect for these embryos' alleged dignity was used to override women's interest in controlling what's happening with their bodies. The UN has declared, for no good ethical reason at all, that reproductive human cloning is dignity violating. This emperor certainly is naked! Human dignity, warm and fuzzy as it may sound, is a useless tool for advancing arguments on any of the relevant fronts in bioethics. This insight is true regardless of the substantive stance that you'd take on any of these controversial issues, by the way. Dignity really is just a rhetorical tool as opposed to a serious conceptual means to advance discussions on these issues.
Today we are probably well advised, should we face the need to make a snap-decision, to reject dignity related claims unless these claims have another rationale attached to them that is based on some other framework. If anything, you'd probably right if you assumed that more often than not human dignity is deployed as a means of preventing people from making self-regarding choices.