Peter Singer, a fundamental reference in bioethics, is an author who draws important issues on the rights to live, to kill and die. The first point that must be taken into account is that he is a utilitarian. In the utilitarian conception it is an ethical imperative to act to reduce suffering in the world as a whole. In this sense, ethics is not restricted to interactions between human beings. It also extends to the interactions of humans with all other sentient living beings.
Ethics is a philosophy of action, which makes systematic reflections on the concepts of good and evil, trying to produce consistent knowledge about our actions in relation to their possible benefits and harm to all living beings who suffer (the sentient beings).
The purpose of utilitarian ethics is the reduction of suffering in the world. If there is something that can be called evil it is certainly suffering itself. For this approach, there is avoidable and unavoidable suffering. The first one must be must be extinguished or at least diminished. For the second one we must make efforts to create techniques or technology to turn unavoidable into avoidable suffering. And, in ethical terms, for a suffering to be avoidable it must not implicate in more harm, in the future, produced by itself. It must produce more welfare without weaken one’s abilities.
The utilitarianism adopted by Peter Singer, in turn, is closely linked to the interests (preferences) of living beings in question. So that it is classified as a preference utilitarianism. The understanding is that, having their vital interests thwarted, some living beings suffer greatly. That is, only the sentient beings have interests. In theory, plants or a fetus less than 12 weeks old, for example, do not have any interest, since so far we do not have any evidence of suffering.
So let it be clear, for this ethical conception there is no sacralization of life, not even of human life. By the way, in modern terms, it does not make sense to sacralize anything. In this sense, the greatest respect is for the interest of each one in relation to himself: to his own body and to his own life. It is ethical, in this case, fundamentally, respect for others and for their well-being, as long as this welfare does not directly cause harm to third parties.
In these terms, therefore, the right to live must be granted to those beings who suffer and are interested in continuing to live, who are aware that they are living beings and that there is death, being able to figure, to conceive of a future time and to plan their own life in relation to the data of their reality.
For human beings, for example, it is important to know that they have the right to live, that other people can not simply attack their life (or the lives of those they care and love) without this having serious consequences. Knowing that the state or other people could give way to our lives (or the lives of the people we love), arbitrarily, can cause much anguish and suffering in all the people, with serious risks of social disruption, which implies in barbarism, the war of all against all.
There is no guarantee of a minimum social organization without the right to live being safeguarded. In this case we would not have a society but groups, clans, isolated and in constant tension.
Therefore, the right to live is to protect the lives of individuals and society as a whole. Even the most nihilistic and detached people, in relation to their own lives, have in some way a moral obligation to strive, as far as possible, to stay alive and well, since the life of a human being is usually very precious to other human beings. When a person dies, others usually stay alive and suffer greatly because of the one that is gone. Some people, when they die, can leave irreparable damage to those who remain.
However, if a person survives in poor conditions, in extreme and irreparable suffering (which is experienced by that person as unbearable), there must be social conditions to guarantee the right to die. If we are not, as a society, able to relieve extreme suffering of someone who does not support to live, we should help this person to die with dignity.
In this approach a consequentialist conception prevails. If the consequence of what we do produces more benefits than harm, this action is generally judged as correct, as the one that should be adopted. So the right to die, the right to euthanasia, the right to a painless death, for those who have a terminal illness or suffering from extreme and irremediable suffering, is the right to end suffering that can and should be avoided. This is an ethics of compassion, empathy, and respect for people's autonomy.
And, finally, the right to kill. There is no way support the simple-minded claim that killing is always wrong, because our survival as a species implies killing beings from other species, all the time. Even those who adopt a vegetarian diet also kill other living things in order to feed on them, or to protect themselves and not get some diseases and perish. In the end, the most important thing is to know how sentient beings, which are under our responsibility, are living and being created by us. And if we feed on them, it is ethically important to have a most painless slaughter possible because we are able to guarantee them a dignified death. Just as we are able to decrease, in our population, the intake of animal protein, which can be largely replaced by protein of vegetable sources.
Finally I must say the ethics proposed by Peter Singer never claimed that one should kill this or that living being regardless their preferences. A moral imperative, a duty, in this conception, is related to the decrease of suffering in the world, which in no way can be settled with prescriptions of mass extinction of humans, as it is claimed by some opponents of his thought. Therefore, as the reasons that have been here exposed, autonomous human beings and aware of themselves (or even those who were once so), owners of their own life and their own bodies, these human beings have the right to life.