There are many great arguments for both sides. But I do want to chime in with my personal experience and why I'm grateful for the prep school program as a diversity program.
Long story short: I wanted to go to the Air Force Academy, but my application was sub-par to many if not a lot of candidates.
I applied anyway.
I was rejected.
I was offered a prep school appointment.
Academics: Homeschooled through grade school, and I completed high school through an online program from home. 27 ACT 3.6 GPA. The reason I did school from home rather than through a public schooling system was because I raised my two youngest siblings while both of my parents worked. We didn't have a lot of money and I wanted to spare my parents the cost of childcare.
Extracurriculars: I was very active in my church, holding many leadership positions there. I was also involved in a lot of community service through my church and through a community service club I started through my online school.
Athletics: I ran cross country for one year (senior) of highschool. Otherwise I had no sports and no access to a gym as I did my school from home and couldn't afford a gym membership. Just to give you an idea... I got 3 pullups on my CFA and I'm a male...
With this resume, I clearly had a disadvantage when compared to candidates that had 4.0 GPA 30+ ACT and equivalent SAT scores, multiple sports throughout high school, team captain positions, eagle scouts, boys/girls state, and more... I had no chance to make it straight into the academy.
But the prep school offered me a chance to improve in the areas I lacked and prove that I was capable to make it through the academy. I am INCREDIBLY grateful for the prep school, and I would have been very sad if my choice to do school from home and help out my parents had prevented me from getting into the academy.
Like I said before, when I entered the prep school my physical fitness was really bad. Maxes for men: 21 pullups, 72 pushups, 94 situps, 8'8" jump, 1:35 run
My PFT score was 180/500. From memory:
3 pullups, 40 pushups, 70 situps, 7'4" jump, 1:50 run
Now my PFT score is 398/500 and my best in these areas:
21 pullups, 60 pushups, 130 situps, 9' jump, 1:50 run
I couldn't begin to express the amount of leadership opportunities I've had here. It's unbelievable how many there are. I am VERY grateful that I was accepted to the prep school and given the opportunity to come here.
The only thing that continues to be a struggle for me is academics. I am holding about a 2.3 GPA right now. The saying that your GPA from high school to the academy drops a whole grade point is definitely accurate for the majority of my friends and I.
I wouldn't say there is no need for a prep school. It may need some refocusing, but otherwise I believe it is an excellent system.