It's absolutely a place to try new things. Sports, Music, Theatre, Clubs, Social Groups, etc. It's much harder to get that experience outside of a place that gives it to you.

Outside of high school where are you going to meet new friends? You made friends by doing the activities that the school provided. Because it found people in the same age range that had similar interest.

Not every high school is the same, but I don't agree with your statement at all.