The key of falsifiability

When I hear people talking about teaching intelligent design, "proofs" of economics, and touting home remedies, I think about what makes something a scientific theory.

It needs to make some kind of predictions that can be tested. A scientific theory has to be falsifiable; it simply has to be the case that measurements could be made that would make it false. When they fail to do so, we proclaim the theory good.

An object falling does not prove gravity. I could just as easily say that things want to be close together, that celestial bodies naturally move in circles while terrestrial bodies want to be stationary on a low-lying surface, and explain everything that way. Data always underdetermines theory, points underdetermine functions, facts never tell the whole story of a case.

So why? The best theory is the one that walks the knife-edge between falsifiable and false. The slightest changes in the data could invalidate it - but somehow, they haven't. Arguments about government policy illustrate the point perfectly; is the problem too much protectionism, or too much free trade? Too much subsidy, or not enough? We can stretch and contrive a complex explanation justifying ourselves, and in fact, pundits seem to do so all the time.

What would it take for you to disbelieve this idea? If you can answer that question, you know whether you're relying on science or faith to justify your belief.