[randartie]

Okay, but there's plenty of highly liquid things to trade. For example the SPY has a spread of 1 penny, same with SPY options.

You mention a potential strategy for manipulating the market like pushing prices to hit stops, well if these strategies are common then it seems there exists a potential strategy to take advantage of this.

It seems like so long as the market's next tick price is not completely uncorrelated from its previous tick price, then there will always be a way to 'beat' the market. The market price is not completely uncorrelated (as you mentioned, there's price manipulation driving it to certain prices throughout the day).