Let's propose a hypothetical. Let's say doing that sort of instruction reduced unwanted teen pregnancy by 10% and reduced the spread of sexually transmitted diseases by that amount or greater.* That's pretty significant. Would it not make sense to want that taught in schools? Sure, there might be some political hurdles to deal with, but if the teaching is effective at reducing damage, then it is desirable.
If the teaching is not effective, then there's no reason to have it.
Here's a counter question for you. If a practice increases the overall safety and well-being of society, should it not be done if it merely offends a minority (as opposed to actually hurting them)? Assume the benefit easily outweighs the offense (e.g. lives saved or significant personal damage avoided vs. feathers ruffled). I am not saying the feelings of a given group should be wholly ignored, but they should be treated as something to work to overcome rather than something to cede authority to.
Regarding the exact concern in question, I do not know how effective that is in particular. Sex education in general is very effective though. Teaching abstinence has been shown to be very ineffective.
*It could be greater since someone with an STD can spread it. Someone who is pregnant does not spread the pregnancy around.