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uh-oh there a lot of social goods related to stock markets and other financial tools. Mostly, it democratizes economic activity, IE it allows anyone to participate in the economy, at virtually all levels.
I'm gonna crib a description from Robert Shiller and say that financial tools (that's what the stock market is, essentially, a man-made tool) are the architectural pillars of accomplishing goals. Also creates a shit ton of jobs, allows counties to cooperate together on a more meaningful level, lots of other peripheral benefits. In short, financial tools are some of the most important social inventions post-industrial revolution.
To be clear, this isn't to say the real effects of allmarkets are all benevolent; as a man-made construction, they need to be properly regulated. Be wary of the rhetoric that market activity is inherently good, rational, just and self-correcting - it isn't (see: housing markets for the past 20 years). But when regulated correctly, stock markets have a widespread benefit to society. There are a lot more details to tangent off into, but that's the big idea. Hope it helped.