Because it would be extremely unpopular, the medical community does not tell the truth about sex. If they would, here are some of the things they would publicize:
1) It is essential to be monogamous for life (barring subsequent marriages), and to have sex only with someone who is also monogamous for life. That's the only way to really practice safe sex. Furthermore, an untold number of psychological problems and suicides would be avoided if people were to avoid casual sexual relationships.
2) The only way to properly follow #1 is to refrain from sex before marriage. Otherwise, your efforts to remain monogamous are virtually doomed to failure.
3) Sexual relations should be avoided when the women is having her period. Cancer of the cervix is almost non-existent in women who strictly follow this rule (and the previous two rules).
4) Even if men have no religious reason to avoid masturbation, it is a very poor way to prepare for marriage, because it trains the person to focus on his own needs instead of those of his future spouse. In addition, some people become addicted to masturbation, or practice it in unhealthy ways. As for married men, it is difficult to calculate the number of marriages that are ruined when man take sexual pleasure "into their own hands" and no longer have a need for their wives. There is no physical need to release semen intentionally, and avoiding this becomes much easier over time (provided all the other rules are adhered to). If there really is such a need, periodic nocturnal emissions will take care of it.
5) Even if men have no religious reason to avoid masturbation, and even if the concerns discussed in #4 are definitely inapplicable, men should avoid using pornography. If they are single, it will warp their perception of women and damage their prospects of having happy marriages in the future. If they are married, it will likely diminish their desire for their spouse and cause serious marital difficulties, if not divorce. In addition, many men become addicted to pornography, causing harm in countless aspects of their lives.
6) It is not realistic, if at all possible, for men and women to have platonic relationships. Therefore, to help prevent violations of #1, 2, and 4, such friendships are to be avoided. It goes without saying that affectionate physical contact between men and women is to be avoided, because it will inevitably lead to violations of several of the above rules.