My "house" comments come from the process that large institutions have the ability to make those millsecond trigger calls where they can invest, and profit on the smaller player's slower moves. Huge moves skimming pennies a trade can add up pretty big. Fair?., probably not, but it is probably more of a competitive advantage (scale and technology) versus the claim of rigging.
Again since I don't I don't day trade, this doesn't bother me that much. 8 transactions a month is a pretty busy one for me.
Something like my speed; for me its easier to pick a good company for holding a few weeks when so much new data comes out weekly. iirc they call us 'swing traders'. There are folks that can make money holding for a few hours at a time but I'm not one of them.