Iceland and Denmark, which have probably the most liberal sex policies in non-3rd world countries, have some serious issues with being that way. Incredibly high abortion rate. Significant number of kids born out of wedlock.
urnotthefather.com/out-of-wedlock-births-by-country
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4852976/
The United States falls middle of the pack in these stats.
Our policies obviously stem from Protestants forming this country, and their beliefs about sex almost being a bad thing.
As for violence, I think it's because people are less likely to act when it comes to violence than they are to act on their sexual urges. Which is likely true. The % of 18 year old kids that are going to go Die Hard on everyone is ridiculously small. But the % of 18 year olds that are going to have sex irresponsibly is pretty darn high.
The issue we have now is that those acting violently have access to weapons that can do more destruction than they did 100 years ago. So these incidents have become a huge problem.