Can you give an example of a "most liquid low-priced stocks" that "sit at a one penny bid-ask spread all day"? Correct me if I'm wrong, but you mean that it's the same penny bid-ask spread right? Like, 10.49-10.50 for 6.5 hours as opposed to a tight spread that moves.

Can you source this:

> If we reduced tick sizes from $0.01 to $0.001, the cost of trading for most retail investors on most stocks would fall by 50% or more.

If that's true, it would seem to imply that trading costs are so low that it doesn't matter.