More speed equals a car that is more dangerous to things that it hits. A slower speed car may present more danger to faster moving things that may hit it, but I'm not responsible for how fast other people drive, I'm responsible for how fast I drive, and the faster that *I* drive, the greater the danger that my car will pose to anything that my car might hit with the momentum that I impart upon it by choosing its speed. If someone hits my car in the rear, then they clearly were tailing too close for the speed they were traveling in the first place, and that is entirely on them... not me. You want to pass me? Feel free... Heck, if you adequately signal your intention, I'll generally even slow down a bit after you've signalled to let you back in front of me if that's the lane you want to be in.
I won't usually be in the left lane on a highway, since highway exit ramps are usually off towards the right, and I generally make an effort to get in the lane I need to be in as soon as it is safe for me to do so, and stay there until I turn off of the road.
I don't drive below the limit either, however.... at least to the same level of accuracy that the speedometer conveys my actual vehicle speed.