What makes economics a weak science, weaker than many other humanities, is the habitual absence of experimental evidence. It's of course hard to have a number of double blind histories of the world economy, yet that is what it takes to be a hard science. If you accept that it never can be (many economists try hard to pretend otherwise!), then you have to accept (again, many don't) that building mathematical models for human behavior (without rigorous validation) is no more scientific then some of the worst stereotypes people have for the social sciences. Yet, economics _is_ a social science, through and through. It studies human behavior. Just because currency lets you quantify and calculate more easily than other kinds of behavior, does not make it fundamentally different.