Since I mention this in my post responding to Al H’s objections comment about assisted dying, it seems worthwhile copying it here. In their book Easeful Death: Is there a Case for Assisted Dying? (Oxford University Press, 2008), Baroness Mary Warnock, a philosopher, and Dr. Elisabeth MacDonald, a cancer specialist and expert in medical law, write as follows about the argument from vulnerability:
So what are the abuses that the Australian, Chris Wake ‘knew’ would follow a change in the law? What is said to lie at the bottom of the slope varies according to the person or the group of people who deploy the argument.
One of the fears most commonly expressed is that, if assisted death were an option, patients in the last stages of their illness might have pressure put on them to ask for it, when it was not what they really wanted. It is not difficult to imagine feeling that one’s children were getting impatient either for their inheritance or simply for
relief from the burden of care, and that one had not so much a right to ask for death, as a duty to do so, now that it was lawful to provide it. There undoubtedly exist predatory or simply exhausted relatives. But it is insulting to those who ask to be allowed to die to assume that they are incapable of making a genuinely independent choice, free from influence. (Indeed, there are people so determined to confound their children, if they see them as vultures hovering over a hoped-for corpse, that their will to spite them by staying alive may outweigh their wish to escape their own pain).
In any case, to ask for death for the sake of one’s children or other close relatives can be seen as an admirable thing to do, not in the least indicative of undue pressure, or pressure of any kind. Other kinds of altruism are generally thought worthy of praise. Why should one not admire this final altruistic act? And it would not be wholly altruistic: the desire to avoid squandering resources, or being a burden is combined, in the cases we are considering, with a sense that prolonging life is both futile and painful. It is idle to try to separate these motives. Part of what makes a patient’s suffering intolerable may be the sense that he is ruining other people’s lives. If he feels this keenly, and asks to be allowed to die, he is not a vulnerable victim, but a rational moral agent. 
This seems to me a perfectly reasonable counter to arguments (such a Al H’s) which think that “vulnerable” people would be endangered by assisted dying laws. The claim that we should not accept the request for assisted dying from someone suffering intolerably, because some people “might” be influenced to request assisted dying when they do not really want it, is clearly intolerably patronising and cruel. It patronises the person who is asking for assisted dying who genuinely does not want to be a burden of their family, and it is cruel to those who are suffering intolerably. Additionally, as Warnock and Macdonald point out, it is difficult to separate these motives, which may often be combined. The trouble is that the argument is fielded only because religious arguments will not fly in this context, so that those opposed to assisted dying will use practically any expedient to deny the rights of those who are suffering and want help to die. Additionally, there are ways of ensuring that people are not being placed under pressure to ask for assisted dying. They can be interviewed by people who can make sure that the decision is one thoughtfully and autonomously made.
It is important to note also (once again) that the very same concerns, if the concerns have any legitimacy at all, arise in cases where requests are made to withdraw life support and other life-prolonging measures, where no question as to legality exists. It is simply special pleading to suppose that these issues arise, if they arise at all, only in cases where positive assistance in dying is requested. Christians really need to make an effort to be consistent, at the very least.