It scrapes that % every trade, every millisecond, thousands of times over. That adds up, and all that money has to come from somewhere.
It would be slightly amusing to see some sort of HFT ban, only to see people speedrun re-inventing HFT as numerous problems unfold, like dad putting in a market order for AAPL on a day it had a VWAP of $185 and having his trade execute at an average price of $690. Or more serious problems like shortages and surpluses of commodities in different locations due to bad price information.