b.rock,
Those are good points to be considered.
However, more often than not, I always encounter campers on the leftmost lane going the speed limit or way less when the slower lanes are wide open. What people do not adhere to is the 'Slower Traffic Keep Right' rule.
This becomes more dangerous in a sense because when people can pass at both left and right lanes, it becomes unpredictable and chaotic. If people are trained to pass only on the left side, this becomes orderly and systematic.
Of course this doesn't mean that one should pass on shoulders or double yellow zones, specially on single lane roads. In those cases, we all have to suck it up and follow the pace at which the car ahead is going.
On double lane roads however, i still think that the left lane should be designated passing lane instead of weaving from lane to lane because a slower car can't stay on the slower lane.
I did spend some time in Europe (Germany, Austria and Switzerland) and passing on the left lane rule is quite effective, even in congested hours. In those cases when traffic is congested, you just follow the pace on the leftmost lane and then go back in the slower lane if traffic becomes lighter and there is an opening on the slower lane.
Whether you drive a truck, bus, car or bike and i agree they all need to pass at some point or another. In this scheme, wouldn't it be so much easier if the left lane were open for them to pass and they could simply go back to the slower lane once they are done passing?
Lastly, have you ever encountered 2 cars going about the same speed (both left and right lane) and effectively blocking all cars wishing to pass? I mean the road ahead is wide open but the car camping on the fast lane is blocking and creating a backlog because he refuses to switch to the slower lane. That does not make sense at all.