This topic is of great controversy here on ecoModder, as detailed in this thread:
http://ecomodder.com/forum/showthrea...ate-26517.html
I'll offer a couple points. First, the perception of danger and safety is often subjective. For example, someone might believe going 5 under the speed limit on a 2 lane road is safe, while another might consider that a risk to head on collisions or traffic jams. There is no red line between MPG and safety. Each situation is different, every road is different, and every driver has their own limits and abilities. The only real standard to follow is the law. As long as the driver knows and follows the written rules, everything else is subjective. Common courtesy and respect for fellow drives is something I practice, but once again that is my own opinion and preference. For example, I would never go 15 under on a 2 lane highway with traffic, even though it is legal.
My second point is that every car on the road is responsible for their own actions. For you to say it's the slow drivers fault that a passing car created a head on collision while passing is just not true. The driver that chooses to pass is the one responsible for safely navigating and completing the pass. Unless the slow driver broke a law, they are not liable for other drivers' mistakes. And as easy as it is to blame the slow driver "forcing the other drivers to pass", no such thing happens. Slow drivers don't force people to pass, people want to pass slow people and choose to do so based on the desire to go a certain speed.