system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What real value does a stock market provide? And what value does high speed trading provide to that market?

Honest question. I don't see how high speed trading is beneficial to society and to a certain degree wonder about trading stock in general. 

Thanks in advance for showing me the way

Edit: thanks for all the response so far. I mainly posted this with the questions of high speed trading in mind. I understand how and IPO provides value initially, but my more general question about the value of a market is about what happens after the IPO. Thanks again for all the responses. 

Edit 2: Lots of debate back and forth about HFT. I think I have a clearer picture of each side of the story. Thanks for all the input. I'm going to mark it as explained (but not because of any one particular answer, a bunch of them together), but feel free to keep up the discussion.
gpt
If you know that you can trade your ownership in a company on an open market you'll be much more willing to invest in that company. More people investing in economic growth is beneficial for everyone as it grows the economy.

With regard to high speed trading it doesn't really have the same benefit.  But there is concern that artificially limiting trades based on an arbitrary definition of what "high speed is" might hamper the market.