The biggest problem is we let too many people live who will never live an enjoyable or fulfilling life.
If someone is born with major defects, or worse, a terminal disease/defect that will result in an almost guaranteed death in their first decade or so of life... why do we let them live? We are such a selfish species and so damned self-centered into thinking "all life is precious" and "my children, no matter how fucked up, deserve a chance to "enjoy life""
If I'm so fucked up I'd die before my tenth birthday, I'd rather not even have been born. Or, not kept alive after birth.
We waste so many resources on keeping people alive that, honestly, do not need to be kept alive.
One of these days I'll get around to making a living will that takes care of the same thing for myself, in the event I ever get into a very slow death spiral of sorts. No more than a few weeks in a coma (unless medically induced and can be brought back at a moment's notice), and none of that long-term care bullshit. If I have to be cared for almost every moment of the day, I'm not LIVING, and I will take my own life at that point if doctors won't let me go. It is futile and a criminal waste of resources and time to keep people alive when the realities of the situation basically state they aren't fulfilling a full life anymore.
But we won't ever realize that, not until it's too late and we've dug our own grave. As a species, we used to practice infanticide when defects were spotted (not regularly, but it happened), but we've gotten so wrapped up in religious morality that it's borderline criminal to even THINK such things anymore.