Nah. Less slow down if everyone was considerate because they'd move left until they reach a lane that is traveling at the desired speed.
Of course, the other required courtesy is that people should always move to the right if they aren't overtaking anyone in the lane to the right. The "slower traffic keep right" rule. Instead, people are hesitant to move right due to all the (usually non-signaling) assholes that pass on the right without hesitating and without giving the slowpoke a chance to move over. It discourages the slowpokes from moving over when they should. Passing on the right when it's not necessary and without giving the slowpoke an opportunity to move-right just makes everyone less safe and it completely disrupts the speed of traffic throughout the lanes.
I can't tell you how many times I'm traveling at 85 mph when I spot someone in the distance behind me that is obviously traveling much faster. I immediately use my right signal and check my right side. As I start to move over, the person zooms right up and around my right without even considering that I might be moving into that lane to get out of the way. No signal, of course. I have to swerve back into the lane I was leaving and the person squeezes through a dangerously tight gap between me and someone just ahead in the lane to my right. As I look ahead, I see them doing it repeatedly and causing near-collisions over and over, even passing on the right when the left is wide-open!
I see multiple drivers behaving like that every time I drive through Atlanta. Oblivious idiots.