OK, so the 12 year old has to get his second molar pulled. If he has the rest of his molars, from what I have learned & observed, it shouldn't be too big of a problem. He will still have 7 other molars at the age of 12 to chew with. In fact, if his third molar in that quadrant is developing normally, that may even erupt when the kid is around 20 b/c it has room to come out now since the second molar is gone. They teach us all the time that people can live without teeth, even without ALL of their teeth. Believe me, we have some adamant patients in our clinics who do just that - they refuse to have or wear their partial dentures b/c they have figured out how to get along fine without it. Missing one molar isn't going to lead this kid to a "lifetime of poor nutrition."
Healthy, vital teeth with no carious lesions (ie "virgin" teeth) get extracted all the time in kids & teenagers with crowding so they can have orthodontics. Usually it is premolars. This doesn't affect their nutrition in any way. Also, sometimes teeth are just congenitally missing - although it is rare that a second molar would be congenitally missing, third molars and lateral incisors are commonly missing (board question!).
Say a kid is biking and breaks off a huge chunk of both maxillary central incisors. Dad brings the kid in, the dentist tells dad that both teeth need root canals and then need to be crowned. Dad is currently in big financial troubles and just can't afford all of this work and dad is in the 50% of the population who doesn't have dental insurance. I don't think any student in my class would tell dad, "Well, then the only other option we have is to extract and leave your kid with a huge gaping hole in his smile." I'm sure the dentist would figure something out so s/he could save the two front teeth.
It is futile to try and compare medical and dental treatments; they are at different ends of the spectrum. An article I just read for class makes some of the following points.
1. Physicians supervise all other health care professionals who call themselves "doctor" but do not attend medical school EXCEPT dentists - an optometrist has to refer complex & surgery cases to an opthalmologist, a psychologist refers to a psychiatrist when neuroses becomes psychoses, chiropractors have to send to an orthopedic when surgery is needed, podiatrists treat things that many dermatologists and orthopedics also see. But if the endodontist can't find the mesiolingual canal on a mandibular second molar, there is no physician to bail him/her out.
2. Medicine has over 100 recognized specialties & 80% of physicians are specialists; Dentistry has 9 recognized specialties and 20% of dentists are specialists.
3. Medicine has many TESTS for diagnosing c\conditions (blood, urine, genetic, ultrasound, MRI, etc). Often, medical specialists are required to interpret the results. Dentistry has 3 tests - a radiograph, a perio probe, and pulp testing - they are all quick, inexpensive, and easy to interpret.
4. Medical treatment is unaffordable for most people. Dental care is very reasonable. For the last 25 years, dental fees and dental incomes have increased at a rate lower than inflation. Yet 50% of the population fails to see a dentist.
The list goes on, but the point is that the two are different, so you can't keep pulling examples from medicine to prove anything about dentistry.