Regarding Economics, it is, by definition, is a social or behavioral science, not a hard science, because it is studying human behavior. Economists like to think otherwise but the logic should be easy to see -- it's studying stuff that people do in a system with other people. This means, again by definition, that there aren't hard and fast rules like there are (sorta....) in the hard sciences. Rather there are a set of predictive probabilities based on what's happened before and based on the logic that actors in the system usually apply in similar situations. Some of these predictive statements have held up pretty well over the years (like, at a high level of abstraction, how supply and demand interact) and some have not (see the "Phillips Curve" controversies) and some can never be tested because the things required to test them will never happen.
I also need to point out that, again by definition, economic activity, far from not being nullified by legislation, would not exist without it. Modern capitalism exists in a world created by legislation. We have roads, schools, courts, law enforcement, etc, all of which modern Capitalism assumes, and depends upon the existence of. The anarchic, Capitalistic-driven fantasy of Robert Nozick simply does not, and likely cannot, exist. As I recall from the secondary literature, Smith seemed to understand this more than do his successors or disciples. I suspect this isn't precisely the kind of thing you meant, but either way, it's an implication.
