So far, this rule of thumb has not let me down.
FYI, you may want to read Feynman's lecture on Cargo Cult Science -- that is avoiding the trappings of science while not actually having the rigour and intellectual honesty of true science. A good link is here: https://calteches.library.caltech.edu/51/2/CargoCult.htm
I enjoy economics, political science, anthropology, sociology, etc, but they are most definately not science.
And this is your whole argument?
Isn't physics a "natural science" and therefore not science according your rule of thumb.
This discussion is stupid. If you want to argue that social sciences are not science, all you have to do is show that social sciences don't follow the scientific methodology. If you can't show that, you should shut up and stop wasting everybody's time.
But in the physical sciences you have well-formed mathematical models that make very specific and precise predictions and can be tested to a high degree of accuracy. That specificity allows you to set threshholds like 5 sigma for acceptance of a result as being verified.
"Did we find copper" is a bit different, and thus there is a fuzziness in history that you don't have in physics or chemistry, which is why we don't view history as being a science even though it benefits from use of the scientific method. Everything -- cooking, dating, gardening -- can make use of the scientific method, but at issue here is the trust that the public places in accepted findings of science and such trust is not justified in the fuzzier fields. People need to add big error bars in their heads when listening to results from social sciences and much smaller error bars when listening to results from physics.
Really you need more modest goals, for example to at least try to approach the subject objectively rather than via sentimental moralizing. Even that is a massive effort. Imagine a physicist decrying how "wrong" it is for gravity to be weaker than the other forces. You would laugh at such a person and immediately classify them as not a real physicist. So you can use that as a filter to exclude much of heterodox economics and economists as a start. That's the battle being waged -- objectivity -- not falsifiability.