Every now & then I've had someone say to me that there's no harm in children hearing about 'other ways of knowing' about the world during their time at school, so why am I worried about creationism being delivered in the classroom?
Well, first up, my concerns - & those of most of my colleagues - centre less on whether teaching creationism/intelligent design is bringing religion into the science classroom1, & more on how well such teaching prepares students for understanding and participating in biology in the 21st century. For example, if a school can make statements like this:
It is important that children and adults are clear that there is one universal truth. There can only be one truthful explanation for origins that means that all other explanations are wrong. Truth is truth. Biblical truth, scientific truth, mathematical truth, and historical truth are in harmony2.
and go on to list the "commonly accepted science we believe in", then their students are not gaining any real understanding of the nature of science. And the statements regarding the science curriculum that I've linked to above indicate that it's not just biology with which the school community has an issue. Physics, geology, cosmology: all have significant sections listed under "commonly accepted 'science' we do not believe in"3. (Did you notice the quote marks around that second mention of science?)
Science isn't a belief system, & while people are entitled to their own opinions they are not entitled to their own facts. Any school science curriculum that picks & chooses what is taught on the basis of belief is delivering (to quote my friend David Winter) "a pathetic caricature of actual science, ... undermin[ing] science as a method for understanding the world and leav[ing] the kids that learned it very poorly prepared to do biology in the 21st century." Or indeed, to engage with pretty much any science, in terms of understanding how science is done and its relevance to our daily lives. And if we're not concerned about that lack of science literacy, well, we should be.
1 although I do think this is a problem too.
2 with the subtext that the first 'truth' takes precedence.
3 Taken to its extreme, the belief system promoted in teaching creationism as science can result in statements such as this:
We believe Earth and its ecosystems - created by God's intelligent design and infinite power and sustained by His faithful providence - are robust, resilient, self-regulating, and self-correcting, admirably suited for human flourishing...
...We deny that Earth and its ecosystems are the fragile and unstable products of chance, and particularly that Earth's climate system is vulnerable to dangerous alteration because of miniscule changes in atmospheric chemistry.
This does not look like a recipe for good environmental management to me.