Do you ever buy or sell stock? Perhaps indirectly, through a mutual fund or 401k type plan? If so, then you benefit from high liquidity in the market. HFT and other Wall Street shenanigans do skim from the top, but they also provide liquidity. It's almost certain that the liquidity benefits small market players more than the skimming hurts them. In other words, the money they're skimming comes from the banks and brokers rather than you and me.
For example, take the stock of Red Hat (http://finance.yahoo.com/q?s=RHT). Yahoo Finance right now shows that, as of the last time the market was open, I could buy 100 shares for $42.56 (that's the "ask" or best current asking price), or I could sell 300 shares for $42.09 (the best available "bid"). That's a bid-ask spread of about 50 cents. That spread is a hidden cost to either buying or selling stock: If you buy and then sell RHT, you will have paid about 50 cents per share just for the privilege, even if nothing in particular happens to the company. Let's split that 50-50 and say that every stock transaction in RHT (buy or sell) costs you 25 cents per share in implied fees.
Those bids and asks are set by individuals and companies who are competing. They want to get a good deal for either buying or selling the stock, but they also know that if they set asking price too high or their bid too low, they'll never make any trades. The more competition there is, the tighter the bid-ask spread will be. HFT and other algorithmic approaches allow firms to set prices on tons of stocks without requiring human attention for each one, which dramatically increases the competition and thus tightens the bid-ask spread.
In this example, if you outlaw HFT and similar trading strategies, maybe RHT will have a spread of $1 intead of 50 cents. Maybe you'll be happy that HFTers aren't making ther 5 cent skim off the top anymore, but it'll be cold comfort when you're paying 25 cents more on each transaction and it's just going to a different Wall Street firm.
If you think I'm exaggerating the effect of computerized trading of the spread, have a look at slide 8 (page 4) of this study: http://fisher.osu.edu/~diether_1/b822/trading_costs_2up.pdf. Starting in 1960, the average bid-ask spread has ben dropping steadily every decade to a small fraction of what it used to be.
Background: I am an actuary trained in quantitative finance. I've never worked in Wall Street or done any HFT or other algo trading.