They have revealed that high speed long distance travel was not common before it was possible. Who would have guessed?

This is exactly how the system currently works. But the key point you are missing is that the HFTers are the exchange. The exchange is operated by the members, which are the HFTers.

If HFT was outlawed, old fashioned cigar smoking brokers would presumably come back, and they would charge fat fees, just like they used to. But the world would continue to turn. I am not saying that HFTers are necessary, just that they are beneficial.

The "flash crash" was NOT caused by HFT. It was caused by "programmed trading" which existed long before HFT, and, in fact, existed long before computers.

No. They are solving problems inherent in markets. By increasing transaction speed, they are reducing risk, resulting in lower transaction costs.

Before HFT, spread were wide, and brokers owned big yachts. Today the old brokers are bankrupt, and instead most of the money goes to the investor, and some money goes into system research and salaries for the researchers. This is a big improvement. Most of the people wishing for the "good ole days" of the trading pits, are not old enough to actually remember them.

It is bad for brokerages, that now have lower profits. It is good for everyone that invests in stocks, either directly or indirectly, which includes nearly everyone with a pension fund or even an insurance policy.

The exchanges are made up of their members. The members are brokerages that execute trades on behalf of their clients. You, as an individual, cannot log into the NYSE computer and execute your trade anymore than you could have walked into the pit during the old paper-based days. So why can't you trade with a "member" instead of a HFTer? Because the members are the HFTers. For all practical purposes, the HFTers are the exchange.

The flash crash was not caused by HFT. In fact, the SEC investigation determined that most active HFTers were trading against the decline, thus making the crash less severe. One of the SEC recommendations was to find a way to keep more HFTers active during big swings because they help to keep the markets stable.

You can! There are plenty of brokers out there that would be happy to charge you extra. Or you could just flush your surplus money down the toilet for the same end effect.

Let's turn the question around: What do you hope to gain by passing yet more laws that prohibit consenting adults from engaging in transactions that you think should be banned because you don't understand them?

Actually, they are middle men that lower the price of the commodity. You should look at the history of transaction costs before and after the adoption of HFT. The have fallen dramatically. If they didn't offer better prices, why would anyone trade with them?

You have a weird mental model of how stock markets work. They have always relied on middle men to execute the trades. The only difference today, is that the HFTers are far more efficient.

This question has been beaten to death every time a HFT related article is posted. But people still ask, so I will try to answer. High Frequency Traders (HFTs) are not investors, they are market makers. They find a willing buyer and a willing seller, arrange the transaction, and execute the trade. They make a profit on the spread between the buy price and the sell price. The problem is that once they locate the buyer and seller, they need to buy the stock from the seller first, then turn around and sell it to the buyer, but the buyer may have cancelled they transaction, or they may have already bought the stock from someone else, in which case the HFT is stuck with the stock and may have to sell it to someone else at a loss. If transactions are granulated to one second intervals, instead of say, millisecond intervals, then the risk of this happening is a thousand times higher , and the HFTs will insist on higher spreads, resulting in lower liquidity and higher transaction costs for both buyer and seller.

Since the introduction of high frequency trading, transaction costs have fallen considerably, saving plenty of people a lot of money. The only losers are the old market makers that used to have lucrative sweetheart deals with the exchanges. Many of those old market makers are now bankrupt. Good riddance.

... and transactions costs go up for everyone. Do you understand that the buy-sell spread has fallen dramatically since HFT became feasible?

This is a problem that is just crying out for a simple free market solution: Just charge slightly less for middle seats, and slightly more for aisle/window seats. Why don't the airlines do this?

I doubt if most people will notice. When making flying decisions, most passengers care about three things:
1. cost of the tickets
2. fares
3. ticket prices
Discount airlines that have cut amenities to reduce costs, have thrived.
Speaking for myself, I have a family to support, and renting a comfortable seat for a few hours is not a priority.
If a thinner seat allows the airline to cut $20 off the price, that is fine with me.

Most big companies do this. Why not? It is completely legal. If America wants more tax from companies that employ people in America, they should just raise payroll taxes. That would have the same effect.