Parent's should absolutely have a say in what children are taught. However this is a delicate and fine line, as it is easy for parents to overwhelm the system and ensure that garbage is taught to the kids because it fits their dogma. It is, of course, possible to swing the pendulum entirely the other way and indoctrinate kids rather than teach them. When these topics stray from the facts and into the realm of opinion, all too often there is no dissenting view, especially in a classroom by necessity dominated by a single voice. We need the checks and balances that a voice from the parent's affords us, without entirely caving to one sides doctrine vs another. Unfortunately in these cases the true casualties are truth and facts substituted with doctrine and dogma.
My daughter, in Jr. High, was asked by her social studies teacher during their section on American politics, to write a letter to then President Bush expressing that she did not support the war. She wrote a letter expressing her opinion that the war should continue as long as it was just and had a clear outcome in mind. We had discussed the topic often in our house and I encouraged the kids to read about these things and form their own opinions, and all of my kids often came to different views on the current events we looked at. She turned in her letter and got her grade back as an "F". When we talked to the teacher she said the assignment was to show that we do not support the war. We had to go to the school board to get the grade over-turned, as the principal agreed with the teacher that we have to teach the kids what is right and wrong in politics as well as in other school subjects. And in their view the war was wrong so that is what must be taught. It turns out of the 60-odd kids she had write the letters, about 1/4 wrote something different than she intended, all got "F" grades, and yet parents of only 3 kids came forward to contest what was being "taught" with this assignment. The grades were overturned, and she found some excuse to miraculously give all the kids she disagreed with "B" grades while all of them that wrote exactly what she wanted got "A" grades, at least from the ones we heard from which was a good chunk of the students overall since we got them all talking about it. We also found out later that she actually mailed all the letters that spoke out against the war, but none of the other letters were mailed.
This was not the only time we faced this kind of thing. My oldest son went to a technical college-prep charter high school in Utah. He had a science teacher who had to go over the section on evolution. He was a staunch very old-school mormon and when he taught it he pulled maybe 10% from the book and filled in the rest about how it was all garbage and God never intended for man to believe it. Someone else got wind of it and a parent again confronted the school. The teacher was not reprimanded or anything as far as we know, but they had a different teacher come in for that section and deliver the material straight from the book.
These are not isolated instances. You can see them all over the news, as some of the quotes above allude to.
This is all just indoctrination of our kids in one form or another, who more often than not do not know better than to trust their authority figures. It is compounded by how often a kid complains about a teacher and the parent just says "look they are the teacher, they are the authority, you have to listen to them", so we reinforce this relationship as parents more often than not. If the teachers are truly looking to get the kids thinking and forming opinions about these topics, that is great. If the first teacher above had asked them to read 3 articles from different sources and form an opinion and write a letter expressing that opinion then graded it on the depth of their research and a logical thought process that would be awesome as it would get them to consider dissenting viewpoints. But so often the teacher does not want dissenting views, they want to teach their own beliefs in a vacuum so the kids can learn what is "important to society" as they see fit. Therefore this kind of **** must be at a minimum tempered, but hopefully eradicated from our school system, from either side. And without parents having a voice this kind of stuff would largely go unchecked.