It doesn't do *crap* for the main alleged purpose of the stock market - investing in worthwhile companies and business ventures as opposed to less worthwhile ones. Basically microtrading is just a way to shave money off of **everyone else's** trades and pocket the difference. Making money by taking it from other people trading, and NOT because you've made a wise investment in a good company.
OF COURSE it results in instability. It takes the irrationality of people's emotions that's already a play in the market, and then it does more emotionally-charged guessing based on that. It's instability squared.
One of the best ways to discourage it would be for the US to just start charging a fee for every chunk of shares traded that's more than, say, 1000. Something like $.50 . That could cut down the profits, AND help pay for some programs to dig us out of the whole Wall St. put us in back in 2008. Maybe even some enforcement for the SEC (imagine that?)