I'm not sure I would say often. The no speed limit stretches are much more limited than people outside of the country seem to think, and often are temporarily limited when needed, times of higher traffic, road work, near cities or on/off ramps, weather conditions, etc. It is not as much of a free for all as you make it out to be.

We already have laws that make people responsible if they are speeding and crash and hurt someone, and people still do it. The problem with your logic of "there should be no rule unless someone does something to hurt someone" is that people are not always rational, and once someone is hurt or killed it is too late. It is better to try and discourage the behaviour that hurts someone before it happens, rather than after.