Going on anecdotal evidence from media such as 'Mad Men' (not the greatest I know) it seems that there was an increase in at risk behavior in the 1950s following WWII. Basically men being interested in smoking, drinking, and sleeping with as many women as possible and not worrying about it later. While I understand that this isn't much different for many people today, and that gender politics probably had something to do with it (that in certain circles it was accepted that men could do certain things like stepout on their SO), has anyone considered that this type of at-risk behaviour may have been a massive societal coping mechanism to the PTSD from the Great Depression and the Second World War?
Not an answer, but a bit of clarification: Mad Men takes place in the 1960s, and Donald Draper is actually a Korea veteran, which is a plot point in the first season. Also some of the at-risk behavior was not considered at-risk to such an extent at that time. Smoking was only starting to get attention as a health risk, which is also a plot point in the show. For example the show shows pregnant women smoking and drinking. From the context it is clear they consider it perfectly normal behavior and not reckless at all, but the scene is grating to the present day audience because of increased awareness of the health risks.
A lot of entertainment value of the show is showing behavior which is considered totally normal in the period but shocking to modern audiences - like littering in nature after a picnic. They didn't litter because they had PTSD or were otherwise reckless, they just didn't have the awareness of the issue. Discussion
As for sleeping around I would question your assumption that this was especially prevalent in the 1950's anyway. I'm not sure if reliable data even exists for this?