I'm not impressed by any teacher who thinks they could ask such a question and not get flack from parents for it. As the parent of three children who graduated from a fairly decent high school school in the conservative, science-skeptical, way too religious sticks, I'd be upset. Not because I'm afraid of talking to my kids about sex or other realities of adult life, but because it's not what I pay my taxes for our schools to teach. Squeeze a bit more science, math and cognitive ability into their brains first, and then we can discuss them taking ethics tests from their English teachers.
Way too many of their classmates were only attending high school because it was a legal mandate, and as soon as they were old enough to do so they dropped out. Our public schools have more important work to do inspiring those kids and their parents to care about learning and their future. Once we tackle that job then we can ask questions about if it's okay to fuck your sister so long as you use protection. Is that really a big problem right now? How about just teach them how to use a fucking condom. There's a subject I'll fight for being taught in our schools.