General Discussion
In reply to the discussion: 5 Reasons It's Just Absurd That America Doesn't Tax Wall St's Transactions [View all]Bernardo de La Paz
(60,320 posts)High Frequency trading does not add extra liquidity to the market, or if it does, it is not necessary in an age of electronic trading. Electronic trading by brokers, institutional investors, and individuals does a very good job of providing liquidity: it is plenty fast enough without adding computer driven HFT.
You correctly identify the role of capital gains tax.
Short selling is a very good market brake. It helps avoid speculative bubbles because the short seller's offer increases supply and drives prices down or slows down a price rise.
Market manipulation is a crime that is independent of short selling. Manipulators tend to buy more than they sell short. They tend to buy up a stock to get momentum going, perhaps with email spam pumping, and then after suckers have bought in, the manipulators dump it by selling shares they actually own.