I dunno, umm
The benefit of having an expert in each feild teach you what you need to know instead of just one person who isn't. The social aspect, friends, GFs/BFs, interacting with different types of people, learning life skills. Field trips, labs, experiments, activities, sports, clubs, it's a whole different experience.
If teachers were experts in their feilds the US would be graduating a smarter populace. You need a teaching degree to teach, not a degree in the subject you want to teach. The benifit of having a teacher(parent) that has all of their intent and focus on making 1-4 four kids graduate is better than the teacher whose intent is a carreer and has 30-90 students.