There should be no need for schools getting into it at all. Schools are not parents.
Who said parents are the only ones who should and can only teach kids on how to live their lives? For an ordered society there needs to be a system of education that goes beyond academics to the overall goal of a child's success in the future.
And you're wrong, schools are like parents, or at least they should be in a way. Regular parents just can't get the job right if they have to divert their time to educating their children when all they need is a safe, unbiased system of education.
With your logic, I could name at least 3 or 4 crucial courses to be null and only a "parent's job". I would like to raise a question such as "Why don't we get rid of school all together? Parents are obviously the geniuses around here and therefore they should be the ones to educate their children about these subjects. Oh, and for the parents who don't know it at all? Too bad!".
If we go by your logic, this society would shrivel down to a dumb, uneducated and misinformed society that only relies on parents to teach kids about some things that actually need to be taught in a more specialized manner.
And in my personal sex ed experience, there was lots of misinformation flying around.
Misinformation? Like what?
And even if there was some sort of misinformation, you think parents will do any better? They would do worse, because they do not have the facts at their fingertips or the research needed to properly understand the human body and its sexual functions. They are more likely to hold biased views about sexuality, like "people should remain abstinent until marriage" or any other religious morals they have.
I don't know what schooling system you went to, but specialists (and yes, they are specialists, no matter what you say) hold much more knowledge about the topic at hand. It would be a tremendous mistake to allow only parents to lead their children's sex lives, since their information is not going to be accurate most of the time or just not enough to fulfill the questions of their children.
By the way, I am not saying that parents shouldn't be allowed to teach sex education to their children whatsoever, I am saying that schools should be permitted to properly educate students since they are much more qualified to do so. Parents in the end should just answer some questions here or there or introduce their children to sexuality before letting them arrive in sex ed class.
A school is a place of learning, but that should not just include academics. It should also include social sciences and topics like sex education or driver's education to allow the students to have a firm grasp on every aspect in life in order to have a successful future.