In my opinion, the main reason that evolution should be taught in US public schools and that creationism/ID should not is because we, in the US, have a tradition of separation of church and state. Evolution is the central theory of biology, the single, coherent explanation of a wide variety of biological phenomena. The vast majority of biologists accept it; the only conceivable reason not to teach it would be because it goes against the
religious beliefs of a minority. Likewise, creation/ID is considered an acceptable alternative by
religiously motivated people, not by the biological community at large.
And let us not forget the reason for separating church and state. Traditionally, Christianity has been a very intolerant religion -- not only demanding proselytizing by its members, but the violent suppression of alternative religious views (even heresies within Christianity itself), and even used to justify the suppression of political dissent.
The main parties advocating the teaching of creationism/ID in the US are a particularly intolerant religious group. They are also working to suppress homosexuality and other forms of sexual expression, reproductive freedom for women, the repression of various alternative religions, and even straying into the advocacy of hyper-free market capitalism, the elimination of social welfare programs and the implementation of police power to control the resulting unrest, and a violent, military-based foreign policy based on the self-interest of Americans as opposed to everyone else.
Also, Rremember that the religious right itself does not actually believe in "equal time" -- what they are really aiming for is to do away with evolution altogether and replace it completely with their religious dogma. If they were to succeed and the non-fanatics were to ask for "equal time" for evolution, they would be the ones saying "f*** you" (and probably throw them in jail, if they could).
In my opinion, creation/evolution is a silly, unimportant debate...except it is an important plank for a group whose goal is to determine what everyone else thinks and believes. Not only is fighting the religious right in this area a way of distracting their resources from more dangerous policies, but when they succeed in this one area, as unimportant as I feel that it is, then they are one small step closer to their totalitarian hegemony over thought.
"Intellectually, scientifically, even artistically, fundamentalism -- biblical literalism -- is a road to nowhere, because it insists on fidelity to revealed truths that are not true." -- Katha Pollitt