A theory doesn't mean a guess in science and by now if you have spent more than 10 seconds in discussion with Atheists or have ever opened a science textbook it has already been explained to you. You are either being dishonest or do not care to know the truth. Just in case you happen to never have been told that a theory in science is not being used in the loose sense in which we employ the term in common speech I will explain it to you. A Theory in science is a model (either mathematical, physical, or conceptual) of predictive capability. The model must account for all data (points of fact) and all laws about the given subject. The sense in which you are employing the word theory is the sense in which science employs the word hypothesis.
Either way, to demonstrate this to you, we have the germ theory of disease. You would not calls the fact that germs cause disease a guess. We have gravitational theory. I doubt that you would say jumping out of airplanes without a parachute and the resulting sudden stop at the end is just a guess. We have cell theory. Are cells just a guess? Ballistics theory. Are we just guessing that a known material will stop a given bullet shot out of a particular gun from a specific distance? Systems theory. Are the resulting computers just a guess? What are you typing on then? In science, a theory is the highest achievement. It is a model that accounts for all evidence and can adequately be used to make predictions that repeatedly come true. Also, it must be capable of withstanding the harshest critique in the peer reviewed process. You fail to take account for the fact that words are being used with the utmost care in science and not in the loose sense in which these words are employed in the general public.