...then eventually medical decisions will be based on projected Return On Investment - to the government. Example: Your 20 year old is worth saving because they have made it to adulthood and have decades of tax payments ahead of them (the area under the curve is huge). It's worth investing some medical dollars in them today to reap the tax revenues tomorrow. But most 70 year olds aren't going to generate much more tax revenue. Likewise, a premature baby is an unproven tax source and statistics say that premees are likely to consume more medical resources throughout their lives, offsetting and perhaps exceeding their tax revenue potential.
In a world of limited resources, which is the better investment? Whom do you want making that decision - family members who might be willing to make personal sacrifices, or a nameless bureaucrat reading from some actuarial chart?