Even though I am a non-trad myself, I think it is an important question to consider. Please stop with the reductio ad absurdum arguments. From the voting age to social security, age and its implications have always had a unique spot in societal debates, apart from issues of genetics/race/sexual orientation/etc.
Whether you agree with it or not, schools already do take the initiative in trying to attain the "greater good." For example, look at policies aimed at recruiting disadvanaged or minority candidates. Generally, the ostensible purpose of this is so that areas that are underserved will get more medical providers. Another example is that the vast majority of adcoms have a non-specified requirement for applicants to acquire many hours of community service. Again, here they are trying to recruit future physicians who will be community-minded. Finally, I will bring up the point that adcoms already do have a bias against much older non-trads (e.g. 40s/50s).
Anyway, here are my thoughts (I'm sure I'm forgetting something) on how the cost-benefit analaysis breaks down for admitting non-trads who are 10-15 years out of school:
Pros:
-Bring unique work and life experiences to the medical school class and the field. I think this is especially valuable if they can contribute in a unique way to the field in a big way, such as through interdisciplinary research. In my opinion, when you get to the day-to-day operations of an attending after 7-10 years of medical education, any previous life experiences, while potentially useful, aren't really a huge differentiating factor between non-trads and the younger crowd.
-Potentially in it for "better" reasons and/or they have had more time/experience to think about it. This could lead to more collegiate personality types, a greater likelihood of going into underserved areas or academic medicine.
Cons:
-The major con, as has been noted, is that all else equal, nontrads will probably spend fewer years as a practicing attending.
Overall, I think the area requires more research so we can acquire more hard numbers on each of these topics.