> Even if involuntary they 'trained' people's social skills and withered away at their acquired/innate social anxiety.
Humans don't have a shred of innate social anxiety except perhaps in some odd pathological cases. Any parent who has dealt with a toddler that has yet to learn to talk will tell you that much. Toddlers who can't speak yet try very hard to interact with their parents and whoever else they meet. They've a fascinating ability to get themselves understood by their parents.
Science will tell you that much too. Humans are basically hardwired to communicate. Intensely. So much so that if you gather a bunch of deaf kids together without supervision they invent their own sign language. [0]
With that being said, kids do learn (or unlearn [1]) things at school. Including how to "socialize" (or not).
[0]: https://www.sciencedaily.com/releases/2004/09/040920071439.h...
[1]: https://www.ted.com/talks/ken_robinson_says_schools_kill_cre...