Many people are diagnosed with diseases in which they'll experience untold suffering and agony before they die. This not only includes actual physical pain, but spending the last few weeks if not years as complete and total invalids, basically imprisoned to a wheelchair or bed with no ability to feed themselves or even breathe on their own without help. Then there's the additional problem of their illness causing untold stress and financial difficulties for their loved ones. Some people don't want to spend the last years of their lives in this way. Why should anyone who doesn't have to face this terrible end themselves get to dictate the decisions of someone who does? Only someone faced with the possibility of an excruciatingly agonizing end should get that choice.
If the person has said beforehand they would rather not live in pain, or as a "vegetable", than yes I would say it is ethical. Many people do not want to live while suffering, and it would unfair to ask that of them. We have no idea how difficult or painful it really is.
If an elderly person is going through severe pain due to disease or illness it should be their decision to die. Who are we to say, stick through it? If a person is experiencing such emotional and/or physical pain it should be their choice if they should end their life. It is easy for us to state that they should not do it because it might get better. But sometimes we just do not want to endure it any longer. Therefore, euthanizing is ethical simply because it can end another persons harsh sufferings.
There is no reason to try to keep someone alive if they don't want to live. The will to live is a very important factor in survival; someone who chooses to die or who doesn't wish to carry on probably won't. It's a waste of time and effort to try to change what is set in stone.
When I say euthanasia, I mean the taking of human life with their consent.
I've assumed a basic belief in rights.
Life is a fundamental human right. It shares the defining traits of such rights, one being their inalienability. We may claim them but cannot morally give them up.
We are obliged to protect and preserve our life, but lack any moral right to give up our life.