Isn't that what happened here? Parents decided that the subject matter was inappropriate for their small children and objected?
No this isn't what happened here. You use the word "Parent" like it is a single all encompassing entity, (lazy thinking, shame on you). Not all the parents complained. But the resulting policy effectivly censors all the children from any facts (not opinions, facts) that happen to be inconvient to not just the complaining parent's own prejudices, but any prejudices that any parent might have in the future no matter how unreasonable. As I infered above, some parents are fallable, thus it is ridiculous to allow every parent the right to censor all discussions in schools. Thus the need for reasonable limits.