Tom, Thank you for allowing me to respond. You raise a very good question; to which, fortunately, there is a very good, and simple, answer: the natural law!
At the risk of acting like the dinner guest who offends his host, I fear this is why I can not support completely your libertarian outlook, as it neglects the primacy of natural law. There are some laws that are not bad (meaning they do not contradict natural law, such as prohibiting murder), but sadly there are a great many, and in particular recently, that are contrary to the natural law. We are therefore in agreement that these laws are bad laws, although you reject them as a libertarian, and I reject them as they are contrary to the natural law. The fact we are in agreement so often only reinforces the number of bad laws….
It is difficult to swiftly summarise what I mean by natural law, so I will rely on St Thomas Acquinas (with thanks to Wikipedia:
natural law is the rational creature's participation in the eternal law, yet, since human reason can not fully comprehend the eternal law, it needed to be supplemented by revealed divine law; therefore all human or positive laws were to be judged by their conformity to the natural law. An unjust law is not a law, in the full sense of the word. It retains merely the 'appearance' of law insofar as it is duly constituted and enforced in the same way a just law is, but is itself a 'perversion of law’
Or in my own clumsy words – natural law is grounded in God’s law, so the true measure of a validity of a law is not the libertarian outlook supporting only laws prohibiting violence or fraud; but rather that a valid law must be consistent with natural law, meaning God’s law.
I would also agree with you and extend this to argue that laws made by a democratically elected parliament are not of themselves ‘good’ laws unless they also comply with natural law – therefore democracy does not, of itself, validate a law as ‘good’. The same applies to the common law (when I studied jurisprudence my strong favourite was not realism, but Hayek’s common law theory) which I much prefer to statute.
With that in mind, I think I can answer your question about the Top Gear Act 2013 : Would killing one of the hosts in pursuance of the Act cease to be morally wrong? The answer to the question is a resounding "no". As you state, that is the answer you need, and (I think) you know it to be right. This leads me to make two bold suggestions which may offend my host – you know it to be right because, ultimately, we are created to seek and require the natural law (which also suggests or proves the existence of God), and secondly, that libertarianism, where it ignores the natural law, is the wrong way to look at things!!