Foolishness. Evolution is a law of nature and a fact.
You probably learned (incorrectly) in elementary school that a theory is better than a hypothesis but not as good as a law. And you probably have heard people use the term even more incorrectly, as in "The police have a theory the murder culprit is...", in the sense that someone has a hunch that may or may not be right. Wrong, and wrong. And two wrongs, as you correctly know, do not make it right.
Here's a dose of reality--a theory is actually an explanation of something that combines facts, laws, inferences, and tested hypotheses. If something is a theory it's repeatedly been shown to be an accurate picture of Reality.
But--and here's the part a lot of people don't get--no amount of validation can ever prove a theory. Scientist, dog love their little pea-pickin' skeptical minds, are always willing to say "we're certain this is the way it is...until we learn there's more to the story than we thought." New knowledge seldom makes old laws wrong (well, okay, sometimes...but very, very rarely); usually ideas refine old ones. Better understanding, a step closer to clearly seeing Reality, is the whole point.
So when someone talks about the theory of evolution--or atomic theory, or the theory of relativity, or theory of gravitation--they aren't expressing reservations about its truth. They aren't saying, "I have this theory about gravity that...." They're saying that, as best is known today, this is the way evolution and atoms and reality and gravity work.
But--and here's the part almost everyone doesn't get—while we can talk about the theory of evolution, we can also talk about the fact of evolution. A fact is an observation that has been repeatedly confirmed and for all practical purposes is 'true.' The fossil record and abundant other evidence including genetics, for example, testify that organisms have evolved through time. Although no one was there to see those transformations, the indirect evidence is clear, unambiguous and compelling—it's indisputable. In other words, you don't have the choice of believing evolution or not; you have the choice of understanding it or not. Reality is what it is; if something is hard for you to believe that doesn't make it wrong. It just means you don't understand.
We all frequently rely on indirect evidence. We can't see subatomic particles directly, for instance, but we can verify their existence by watching for telltale tracks that the particles leave in cloud chambers. The absence of direct observation does not make physicists' conclusions less certain. We don't have to see a live dinosaur to know they existed.