Lol, carpe vestri vita, I love the way you phrase your last two answers! I agree. It's funny, high achievement scores and demonstrable skills seem to be the Holy Grail of traditional education, and what purpose do they really have? Nothing much.
I've been thinking a bit about my answers. Here are what I've come up with:
Students should:
think for themselves in order to be able to find and recognize truth.
acquire a love of learning in order to find joy in learning and doing new things throughout their lives.
seek excellence in order to establish a pattern of seeking to improve throughout their life.
be able to read in order to have fun and learn.
write and do arithmetic in order to communicate information to others.
attain high achievement scores in order to brag.
acquire demonstrable skills in order to achieve in their life's work.
exhibit courtesy in order that the world becomes a more courteous place.
All of these would also include, "and to improve the world by encouraging others to do the same." There is also another level of "why" that ends up being very religious, so I decided not to include it; it probably wouldn't apply to most people. But it does give me lots of things to think about when teaching my children.