If you're going 70 and the person in front of you is going 60, then you still need to pass them and it's fair to pass in that situation. You should try to time it so you aren't cutting off someone in the passing lane to do so, but sometimes you pull out and are passing and then someone comes up out of nowhere at 90+mph and you're stuck for a little bit.

Those people cruising at 90mph in the passing lane aren't using it correctly themselves.