Try taking ethics. If we followed your slippery slope logic we'd start killing people when they hit retirement age. After all, they'll never again go back to work and 'pay back' their value after they start collecting social security. Same for the mentally retarded, just drown them right?
"Realistically we need to start realizing that not every person DESERVES the best treatment". And who decides that?
New procedures are always expensive, do you think the first x-ray machines were worth the cost to say "yup, you got a broken leg son". Now they are standard practice.
"so costly that society can never regain that investment". Public education is costly, if a kid isn't learning and behaving by second grade should society perform a retroactive abortion? After all without an education they'll just be a burden on society, and its not worth paying for the education if they aren't being productive, why not save the money for the other years of school?
Did you have a 4.0 GPA in school? what about college? How much are you contributing to society now? I'm not so sure I am getting back my investment in you. Most of the education system in the world are funded by tax dollars.
What about no child left behind? Why don't we get real efficient and just let them starve? They'll never pay enough in taxes to 'regain investment'.