Well, guess what, Creationists, "gravitation" is only a theory, too. We have only empirical observation and some supporting mathematics to support that gravity works, and how it works, but not a scrap of evidence as to "why" it works. No one has ever detected a gravity particle, gravity wave, or gravity packet. Would you leap off a tall building in the hopes that gravity was "just a theory"?
One would think the Germ theory of disease was generally accepted. One would be wrong. Despite manifold demonstrable evidence, there are many people who persist in attributing most human disease to subluxations of the spine, or poor nutrition. Christian science holds that all illness can be treated with prayer.
Of course, there are many illnesses that, so far as we know, do not conform to the Germ theory, but the theory is well supported and there is ample evidence showing it to be applicable to infectious disease.
The theory of gravitation is notably lacking in pysical evidence; however, so far as can be observed, it is a universal phenomenon with no exceptions. Evolution occupies a middle ground. There is substantial physical evidence. No exceptions have been discovered, but, on the other hand, it is hard to observe "evolution in action." For those that can't wait, I would be glad to stage a personal demonstration of the principles of gravitation. This way to the roof--.