A friend was trying to convince me that high frequency trading was a good thing because of the liquidity it added to the market would allow me to sell my stock in milliseconds. If I've been holding a stock for twenty years, when I go to sell it, do I really care if it takes twenty minutes instead of twenty milliseconds? From the look on his face it was obvious that in his world investing in stocks long term is completely alien. Can't be too hard on him though, he did warn me of the Great Recession months in advance, with problems he was seeing in credit default swap pricing being what he considered the Archduke Ferdinand of the financial system.

> If I've been holding a stock for twenty years, when I go to sell it, do I really care if it takes twenty minutes instead of twenty milliseconds?

I think you may care actually. To give an example, I was holding a stock for several years that recently went up in price quickly, without much change in the underlying business. Simply, analysts started changing their rating on it. When this stock got high enough, I started to feel nervous, and I was watching the market open on a day when I was prepared to sell. Immediately, the stock started to tank, and I sold it right away.

I sold it at a good price, and even though I was a long term investor, I made a short term decision to sell based off the (IMO) extremely irrational price.

"do I really care if it takes twenty minutes instead of twenty milliseconds?"

No, nobody sensible cares. But the stuff people are suspicious of is supposed to be regulated so that your executions are only improved. If somehow this isn't true, it should be a bright line crossed and a big scandal with people going to jail or at least big fines.

Then again, if you panic over a "flash crash", then I guess you should be concerned about liquidity?

I don't mean to imply that it's meaningful to them, but I think it's meaningful for this audience.