Sex is complicated. Sex is not always a beautiful expression of love between committed partners. Sometimes it's a casual pursuit of pleasure. Sometimes it's a whimsical act of exploration.
In many cases sex is the direct cause of much sorrow, misery, and emotional damage. Maybe your partner cheated on you. Maybe you got pregnant and your partner left. Maybe alcohol was involved. Maybe you are lonely and got addicted to pornography. Maybe you didn't use contraceptives and are now seeking (or went and got) an abortion. If you look around in poor communities, you'll find a big source of poverty is... unprotected sex. It turns out, you can pretty much ruin your life as a teenager and guarantee you'll stay in poverty your whole life if you get pregnant and have a baby while you are in middle school/high school.
Unlike war and murder, sex is something most people will participate in (in some form or another). So I would argue that it's more important than ever to consider the types of sexual messages we send in media. Do we want to promote sexual relationships between committed partners or do we want to promote wanton promiscuity? I would argue that whichever you choose will have an impact on some non-negligible % of the future choices of the viewers. To be clear, I think we also need to be careful of depictions of extreme gore/violence as well, but for slightly different reasons.
In general, I'm of the opinion that implicit > explicit for both sex and violence in media, but perhaps there is a time/place for being explicit (i.e. so people understand what really happened during the Holocaust, etc).