Have you read equivalent textbooks in other fields to see their treatment? It seems the only criticism we see here is of biology texts. I suspect that criticism is based more on religious sensitivity to the results of evolutionary theory than actual approaches in biology texts as opposed to other fields, but it has been a while since I perused them, so...
By the way, evolution is both a fact and a theory. The fact part is that each generation is slightly different from the one before it. The theory part seeks to explain these differences, and their effects through time.
I'm not arguing against evolution (and no, I haven't done any in depth reading of other texts, sorry!). My point is that if a parent is adamently opposed to their child learning about evolution, then it would be difficult for them to be in a HS biology class, period, as it is just an intrinsic part of the curriculum. Of course, I am for vouchers, but that's a whole other thread.
susie