Our friend and colleague Alex Tabarrok recently wrote this depressing blog post reporting that “freedom in the world is in decline.” But how does one even begin to measure something like “freedom,” and even if one could measure such a thing, what would the optimal level of liberty be? Although we agree in principle with John Stuart Mill (“On Liberty”) that one should not be free to harm others, the harm-principle doesn’t solve the liberty problem (how much or how little liberty is the right amount of liberty); it just raises a new and possibly even more perplexing question: what counts as a “harm”?
image credit: learnliberty.org
prior probability 
What counts as harm, and what actions should be taken by whom to protect one from it? This was one of Asimov’s themes.
Excellent point … We could transplant Asimov’s Three Laws into political philosophy!
Just remember that he went on to write a whole series of stories about how the laws didn’t work or could be subverted.