The original purpose of the market is price discovery and liquidity. Short term trading fits both purpose remarkably well; after all, market makers themselves are short term traders.
As for the issue of Social Security, once again, people who derive their income solely from stock trading are not even covered under Social Security benefits (under current tax code, capital gain is not "earned income" regardless how much work is done in analysing stocks) why should they be forced to pay into a self-help system that doesn't help them at all?