You can argue that a law achieves a good end (on utilitarian grounds, for example) without arguing that it ratifies any particular Natural Rights.

For commercial law there is the obvious test of whether the law leads to prosperity. Can we have a utopia in which our favourite artists, well funded by copyright royalties, are free of the tyranny of the day-job and may create full time, unfettered by copyrights on existings works that they wish to improve, rework, remix, play-off and a dapt? Probably not, but the problem we face is clear enough: construct a system of commercial law around the trade-offs that lead to artist abundance.

There is an Economics and Law movement, partly inspired by Coase's Theorem, http://www.daviddfriedman.com/Libertarian/The_Swedes.html, that has high hopes of economic efficiency as a basis for discerning between good and bad law.