Earlier quoted context omitted.
I really hate to go down this road because it's been rehashed thousands of times on Hacker News, but high frequency traders add value to the market by adding liquidity (and therefore reducing spreads --> cost to you for executing) and price discovery.
Sort of. If you are buying or selling a lot of shares it's quite a bit more expensive. That probably doesn't matter to you or I if we are buying AAPL because it's a small number of shares, but it does hurt any index/mutual funds you're invested in. Norway's sovereign wealth fund (one of the largest in the world, they own 1% of all US stocks) just came out on this exact topic: http://www.efinancialnews.com/story/2013-…
But great for you! Because maybe you're the guy selling MSFT shares to them. You get the benefit of the price rising faster.
The market is more efficient. Norway can no longer take advantage of the fact that it knows that there's all this additional demand (originating from itself) and it takes a while for everyone else to figure that out.