While there are probably sex ed materials that I would find age inappropriate or otherwise offensive, I take a dim view of demonizing the entire process, or demanding abstinence only curriculum.
To briefly summarize the history involved, early Americans were exposed to sexual information at a relatively young age. Rural children would have been around animal mating activites, many times also living in a dwelling so tiny as to make parental privacy in such matters all but non-existent. Early American cities had extremely high (~20% of women) number of prostitutes, sometimes complete with European-style licensing. Even pornography and birth control were widely available by the civil war. For that matter, in 1830, between 30 and 40% of brides were coming to the alter pregnant. The Comstock act and demographic trends did a great deal to reduce the average American child's exposure to scientific sexual information (and probably cut severely into the abortion rate). However even then, there is little doubt from the number of teen pregnancies in, say, 1957, (double that of 1983.) that teenagers were exposed to sexual information or at least having lots of sex. (I can add more cites if anyone wants them).
This history of sexual information being known to children, seems to make efforts to shelter children from information about sex pointless and counterproductive. I know a number of conservatives that argue that children simply shouldn't be exposed to sexual information, basing this on some mythical, non-existent time in the mid-1950's where purportedly children never heard about sex, and therefore refrained from sexual activity until marriage. I simply find it historically indefensible to argue that children were or are better off not learning about reproductive biology. I do recognize that reasonable people can disagree on exactly what materials to teach children, and at what ages. Having said that, I personally have nothing good to say about "abstinence-only" curriculum.
Frankly, statistically, "abstinence-only" curriculum doesn't seem to work well. Western European nations have a radically lower teen pregnancy rate than the United States and they certainly aren't using an abstinence-based curriculum. (For that matter, the teen abortion rate in Western Europe is radically less than in the United States, which is highly interesting when compared to statistics on church attendance.) Note, I have no problem with sex ed material that includes abstinence based materials, only with material that would meet the federal guidelines as abstinence-ONLY.