To the second question first: Extensively, in fact, especially in its most recent guise, intelligent design.
To the first question second: Several reasons. First of all, the controversy surrounding evolution is entirely political; there is no scientific controversy whatsoever. If over 99.9% of scientists in the field in question accept a theory, it really should be taught as the best that the scientific community has to offer. Teaching an "alternative" like creationism gives the impression that the scientific consensus regarding evolution is weak or disputed, which it is not.
Secondly, the "alternative" in question is not only unscientific, but clearly religious in nature, and thus teaching it in public classrooms violates the separation of church and state.
Thirdly, and perhaps most importantly, most people aren't intelligent enough to distinguish good scientific theories from bad ones. That's why we try to teach children how to do so in school. If we let them think that something like creationism counts as a valid scientific theory (especially at a young age like fourteen, the typical age at which evolution as a biological theory is introduced), they won't understand how to critically analyze science or pseudoscience, and may not even understand the difference between the two.
An aside: Recently some intelligent-design pushers have been trying to pass legislation which mandates critical thinking instruction regarding evolution--I think there was a bill in the Louisiana legislature, specifically. You might ask, why would we oppose such a bill, if we are so keen on teaching children critical thinking? Primarily because most of the people pushing such bills are going to try to use them to sneak creationism and ID straight into biology class without really applying critical thinking at all (a variant on the "wedge strategy" promoted by the Discovery Institute). If such people were really interested in critical thinking, they wouldn't be fighting evolution in the first place.
