Speaking a few sentences in front a classroom sized group is pretty normal and kids should be exposed to it. Uncomfortable experiences are a part of growing up.

Both are very important. Not being able to speak in front of a group can change the trajectory of your entire life. Children especially should have as many paths open as possible for when they're ready to decide which one to take.

Both can bring out social anxiety

Generally speaking, socialization is like a muscle. You have to use it to build it. Which is why we have schools introduce people to social settings in controlled settings and with incrementally more difficulty.

"Nobody should ever have to interact with more than a handful of other people at a time" is a recipe for building a population of socially anxious people.

When you cloister kids at a young age, then introduce them to a big school full of more advanced students, you're throwing them into the deep end of the pool late in the game. But just insisting "they're 11 years old! they'll never be social! lost cause!" is infinitely more cruel than weening them into society as best as your system can.

Yes, and a lot of shit you have to do socially in life is going to be disingenuous. I hated it, I still hate it, but I've also seen it used well as a way to at least ensure everyone has spoken before a discussion group. It's an icebreaker, it's not supposed to be deep talk, it's supposed to mean there's a chance that everyone has at least heard each other's name once before

I have had to participate in a "Everyone introduce themselves" like five times at a job I've worked at less than a year. I don't enjoy it, and I don't think anyone does, but it's also important to know who the people you are working with are. Would I ever do it if I didn't have to? No way. But I do. And practice has made it easier at least.