Additional evidence that HFTers are not stealing from speculative investors:

Anyone can start a market. If HFTers were stealing pennies someone would have come along and started a market that banned HFTers (or changed the rules to otherwise get rid of them). Then all of the speculative investors would use this market instead since they could be assured that no one was siphoning off pennies on every trade. Eventually markets with HFTers would shut down due to a lack of customers.

The fact that this hasn't happened has to be considered evidence that the HFTers are, in fact, providing value to speculative investors not the other way around.