In fact, it would be highly dangerous to go 55mph. You'd get rear ended in no time not to mention road rage.
In the presence of lawbreakers like the ones you describe, driving is unsafe at any speed. But don't worry, getting rear ended with a closing speed of 15 mph (the difference between 55 and 70 mph) is much safer than a side impact collision or a head-on collision.
On the Autobahn, it's perfectly safe to drive the speed limit while others whip around you at tremendous speeds. The reason is because slow moving vehicles stay to the right, and fast moving vehicles always pass on the left. Consistency is good for safety. So the moral of the story is, if you're going slower than the normal speed of traffic, stay in the right lane. In fact, it's the law in some places.