Hi, Teets, and welcome to EvC.
Here is my view.
I agree that a person can live a normal, happy, productive life without knowing anything about the theory of evolution. I will list the reasons I think it still must be taught.
(1) Knowledge is its own justification. People should be widely educated, and should know something about a range of fields just because it is a good thing to be widely educated. The theory of evolution is an important part of science and general, and should be part of the biology curriculum for that very reason. Now, one cannot know everything, and one cannot take every single class in school. If one can meet the official standards of a liberal arts education without knowing much biology, so be it; however, one cannot claim to know much biology without understanding the role the theory of evolution has in it.
This is probably the most important reason it should be taught. Like any other subject, it should just be taught because any knowledge in any subject is a good thing, regardless of how useful it is.
(2) Another important reason is that creationists are liars. Maybe the average creationist in the street is sincere in her beliefs, but the major creationist actors are liars. Answers in Genesis and True Origins and the others are full of lies. Not simply different interpretations of facts, but made up facts. Distorted facts. Mischaracterizations of the arguments made by scientists. And these are very obvious "mistakes", and they are told of the mistakes time and time again, and yet they repeat the same untruths over and over again. If they are not deliberately telling falsehoods, then they are choosing to remain willfully ignorant, which is the same as lying in my opinion. The lie openly, they lie shamelessly, and, in the words of Gary Hurd, they lie even when their arguments are undermined by the lie.
I believe that it is we have a duty to look a liar in the face and tell them that we know that they are liars. We have a duty to explain to their audiences the lies and what the truth actually is.
Related to this is the fact that children do not deserve to be "protected" from the truth. If they decide on their own to be creationists so be it; I will be the first in line to protect peoples' rights to believe what they believe. But we do a disservice to children and everyone if we allow them to make their decisions based on mischaracterization of fact and lies of omission.
(3) Less important, in my opinion, but still needing to be said is that creationism does not exist in a vacuum. Although I am ready to believe that most creationists just want to left alone and practice their religion in peace, the major political actors are just that: political actors. Creationism is just one facet of a wider agenda to restrict other peoples' rights to believe what they do and to live their own lives in peace.
These people do not want to protect the sanctity of marriage -- they want to throw homosexuals in jail. They do not want to protect the unborn -- they want to restrict sex completely to religiously sanctioned heterosexual marriages and restrict its purpose to procreation. They do not want all views equally expressed -- they continually demonstrate not only a rabid desire to force their beliefs on others, but they want to prohibit as much as possible contrary views. They restrict behavior, private as well as public, to a very small set they find acceptable; they would even limit political discourse and debate to within a very narrow range of acceptable viewpoints. These people want to impose a Christian version of Sharia on the U.S., and creationism is simply one facet of their overall agenda. We fight creationism as part of a larger fight to protect overall the right of people's life, liberty, and the pursuit of happiness, including the right to determine how they shall pursue their own happiness.
"We must respect the other fellow's religion, but only in the same sense and to the extent that we respect his theory that his wife is beautiful and his children smart."
-- H. L. Mencken (quoted on Panda's Thumb)
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