Reaction time is lowered the faster you go. If you've got someone doing the limit at 65mph and you're doing 85 miles per hour in the lane to the left and heshe decides to pull into your lane to go around the vehicle that's going slower in front of him you will close the gap a lot faster and possibly might not have time to slow down or avoid hitting that vehicle. It may not be right that they pulled in front of you but it happens all of the time. Technically they are in the right as they are faster traffic than what's in front of them. When the signs say "Slower Traffic Keep To The Right" it is meant for the people who don't do up to the speed limit. I'm playing Devil's advocate here.

I feel comfortable driving 100 miles per hour. Heck I feel comfortable driving into oncoming traffic as I used to do that when I was a medic. Does that mean I should do it? When I had my Bonneville SSEi it could easily handle it but I didn't....well 2 or 3 times but only to pass people where I-80 merged from 3 to 2 lanes. Now I just shake my head at the people who do that and wonder what the hell was I thinking before.