The word THEORY means something different to scientists than it means to non-scientists.
What most non-scientists consider to be a theory is what scientists call a HYPOTHESIS: a concept that must be tested before it can become a theory.
Once tested, if the results are positive, the hypothesis becomes a theory.
A theory is the best explanation for a given phenomena available to date. Evolution cannot be tested in the same way gravity can: we cannot set up a situation where Planet A has evolution and Planet B does not. We can, however, test gravity by dropping things again and again: in a vacuum, in water, in air at the normal pressure.
Gravity has become something more certain than a theory, it is now considered a law.
Of course, at high velocities and in certain anomalous situations, it does not always work as expected.
Concepts like Creationism are what we can call speculation: I do not think there is adequate evidence to call Creationism a hypothesis.
The idea that the universe is about 6000 years old, is pretty easily to disprove by geologists, astronomers and physicists in a variety of ways. It seems that most people in this country still regard Creationism as fact, though I don't think most have given much thought to more elaborate ideas, such as the 6000-years old Earth idea.
Many DO seem to agree with the statement that the Bible is (a) the word of God, and (b) true. Many believe that is literally true, but such people have generally not dedicated much thought to what "literally true" means. Does the host really change in chemical composition to human flesh miraculously at the moment of Communion? Does the wine (or grape juice) actually change to Jesus' blood miraculously? Could we submit it to a chemical analysis and find that it really is human blood?
Can we all expect to see the holier among us be sucked up to Heaven in the Rapture as if by a Great Holy Electrolux in the Sky anytime soon? I know people who say they believe exactly this, although they disagree that the Rapture should be described using the word "holy electrolux".