[mironathetin]

"If you let someone merge, make their exit, pass you, you're enabling flow."

yes and no.

If you let someone merge in heavy traffic, and (s)he has to break hard right after merging, the flow stops. This is what happens - indeed - in competitive driving. In my city people seem to be so full of adrenaline, more before than after work, that it happens all the time and already in the morning at 6:30.