If you feel that norm needs to change, and that children should in fact watch hardcore pornography without anyone batting an eye, you may certainly work towards those changes. But you should expect resistance because that norm is powerful.
Actually, Alfred Kinsey did some stuff as bad or worse with children, and yet his work has become the basis for an entire field of study. (It was so bad that a movie had to be made defending him.)
there are plenty of full grown adults who are irresponsible with sexual activity (spreading stds, unwanted pregnancies) so can we just agree that MAYBE middle schoolers shouldnt be exposed to so much sexuality? that maybe a 14 year old has no chance of grasping the consequences and responsibility of sex?
[0] http://www.mirror.co.uk/news/uk-news/how-early-you-lose-your...
You are assuming exposure to sexuality in media is what causes young people to have sex? I think sex have existed longer than mass media.
One also might say that the pill had something to do with the change.
About 2-3% of Adults in England get an STD [0], so 97% are at least responsible / lucky enough to avoid them.
Educating the 14 year olds is the only way - you can't stop the rest.
[0]: https://www.theguardian.com/news/datablog/2010/aug/25/stds-e...