I don't think the cost is necessarily negligible. If the system is setup in such a way that there are those who benefit from every trade, skimming fractions of

I don't think the cost is necessarily negligible. If the system is setup in such a way that there are those who benefit from every trade, skimming fractions of a percent per trade, those add up. They are effectively shrinking the market capitalization of that stock... and over a long period of time that could be significant. If a stock's losses to this are in the range of 3% per year, over a 25 year period the stock will lose 50% of it's market cap from this activity. That's fairly significant.