Long before modern civilization, tribes of hunter-gatherers were the prevalent societies. Their year-to-year survival depended on the group's ability to provide food for everyone. People had specific roles to perform, largely dependent on gender and age. In times of plenty, there was food and supplies enough for everyone, and the numbers could grow. Come times of famine and hardship, necessity served as a cruel master. Since the able-bodied adults were those who provided the food, feeding them was first priority. Should they perish, the entire community would soon follow. Children, who were the future of the tribe, came later and got less food, and the old and infirm, though valued and revered for their wisdom, would often go hungry.
If times of hunger lasted long, the old would die, followed by the young. For the tribe as a whole to survive, this was necessary. New children could be born in the future, and the hunters would eventually grow old themselves, but survival in the present was the primary concern, and so the death of the old and weak for the good of the community was a part of life.
In some societies, as with the Inuit, the old would recognize that they no longer contributed to the tribe, and that their inability to keep up would hinder the good of all. They would deliberately choose to stay behind, letting the Arctic cold put them into a final slumber, thus benefiting the tribe and their families by removing a burden on limited resources.
These ancient applications of euthanasia were rooted in the survival. The deaths of some individuals were necessary for the people as a whole to survive. Here euthanasia was ethical, as the individual placed the good of the many ahead of the good of the one. There was a noble ending for an individual who could no longer contribute to their society.
In modern society, things are different. People pay taxes. People pay taxes so that there can be welfare, health systems, social security, and various other assistance programs. The social contract that is implied here is that by paying into the system for decades, the system will be there to provide for the needs that arise in old age. If people pay into the system, and are then denied care in their infirmity, what was that investment made for?
Modern society has risen far beyond the subsistence level. For most, the daily goals are not about survival. Food and clothing are readily available. The desire to own a bigger TV presents a bigger incentive to work hard than does the need to earn the next meal. Survival is taken for granted. Luxury is the goal now. Our society is wealthy enough that it can care for its elderly and infirm.
Technology has made it possible to care for the old and the infirm. Ailments that would have been lethal centuries ago are treatable, and recovery rates are high. Even when recovery is not assured, we can often manage survival, employing drugs or machines as needed.
Whereas in the past, the elderly could offer little to the survival of their community, today's world welcomes the creativity of the old, the impaired, and all others who would have been allowed to die in ancient times. Through art, computers, knitting, and any number of activities, they can participate in and contribute to society at large.
In modern society, euthanasia is completely unethical. It is wrong to put personal luxury before the survival of others. In any society, survival is paramount, and if people are willing to overlook this out of their own greediness, they create a fearsome precedent. If even a small percent of the population can be abandoned so that everyone else can pursue wealthier lives, the path must eventually lead to the very few who can pursue the most ultimate of luxuries, leaving the many who remain to struggle for their very survival. The most frightening thing is that this trend is already present today. Statistics that show a few percent controlling more than half the wealth are an indicator that we are indeed shifting this direction. We may not be willing to outright kill the weak, yet, but placing our own desires before others' needs still leads to the unnecessary destruction of their lives. Euthanasia? Murder? It is a failure to respect life, and that is always unethical.