Quote from bbqbbq:
you're absolutely right. daytrading gives only liquidity.
It also gives price discovery i.e. making sure the price is clear and most accurately reflects the sum of all available news and information as often as possible. The more active speculators competing for profit, the more efficient the price will be on average, thus the greater the chance that an investor/hedger gets a fair price rather than an artificially high or low one.
If a market trades by appointment and has a 10% wide bid-offer spread, any private investor buying or selling gets raped i) on the spread ii) because the price is opaque and he has no idea if news is out and reflected in the price iii) because he can't do volume without shifting the price. An active community of short-term traders in the stock means a narrow spread, a clear and more accurate price updated in seconds not minutes or hours, and more volume to be able to trade with.
Liquidity also affects end-users of markets. Illiquid assets almost always trade at a significant discount to liquid assets. People prefer something they can cash in at close to fair value if they need to, over something that might take ages to sell, and distort the price heavily if any big volume were done. Thus illiquid shares will trade at lower valuations than liquid ones. This means companies who issue shares will now have to do so at lower valuations to compensate for the illiquidity. That makes capital more expensive, which means lower investment, lower productivity, lower employment, and lower growth. Is this worth it across the whole market economy and stock/futures markets, for a measly $100 bln? The economic effects would amount to way more than that, and the tax may actually *reduce* overall government revenue, thus not only making the tax worthless, but destructive.
If you can't see the benefit of that, you need to study more about markets, economics, investment and their benefits. That's why the west is rich and N Korea and Cuba are poor. The richest countries have the largest number of speculators, traders, hedge funds, financiers etc. That's not a coincidence.
Finally, there's the not inconsiderable point that it would destroy the livelihoods of hundreds of thousands of people who trade markets actively or work for institutions that rely on and facilitate that business. THis would also have major knock-on effects on the local economies of financial centres, and the USA's pre-eminence as a world financial centre. It also has serious moral implications - you are putting people and families out on the street, when they have done nothing wrong. They pay their taxes and follow the rules like anyone else, why should they get hit when they have a viable occupation? Daytraders didn't make LEH or BSC or AIG make insane gambles with 30-1 leverage, why should they get the brunt of the punishment?