S.P.A.O., I could be facetious and suggest that grammar would be better taught in schools than intelligent design.
There are two problems with intelligent design:
The first is that there are countless things that you can point to which do not look like they have been designed, from fish at the bottom of the ocean with misshapen skulls from actually having two eyes on one side of the skull to the appendix.
The second is that it doesn't seem to be too intelligent either. The HIV virus, tsunamis, and tornados don't appear to be too intelligent a solution to anything in my eyes.
Now for evolution. To reject evolution, you have to reject that you are more likely to reproduce if you have a genetic advantage, reject that offspring resemble their parents, or you have to reject that you can get chance mutations. The first is blatantly obvious, the second easily observed and the third scientifically verifiable. From thereon it is purely statistics.
In addition, we have seen evolution occur, among viruses, among moths in polluted towns (which have become black through mutation to camouflage better) and among dung beetles.
Hence it is scientific (if you want to claim that Darwin himself didn't present sufficient evidence, read his works first, please)
2. Is just a restatement of 1. and equally stupid
3. You think it is only "fair" to teach both because there is no way that you can argue against teaching evolution. We cannot be "fair" about how we teach. We cannot teach the epicurean hypothesis alongside Big Bang theory, we cannot teach French and English in an English lesson to be "fair", we cannot teach both Newton and Leibniz's notations for calculus to be "fair". We cannot teach every rival theory on anything, and we mustn't teach as equals theories as unequal as evolution and "Intelligent" "Design". It is to mislead people to suggest that "Intelligent" "Design" is a science. It is to mislead people to suggest that "Intelligent" "Design" is equal to evolution in merit, and it is wrong to mislead children when at school.
But I would love to be fair on this matter, genuinely fair, and give time to both in a science class. That is important to teach science, because then we can explain to children what is and is not science. We can explain why "Intelligent" "Design", why the Flying Spaghetti Monster, indeed why any theology is emphatically not science.