When it comes to STIs, unless a government representative is monitoring state-sanctioned, laboratory-controlled intercourse, people have to be held responsible for their choices and be reminded of the consequences of their actions.
But with myriad resources available — online, doctors, clinics, universities, colleges, governments and non-profits to name just a few — there is little excuse for adults not knowing this stuff.
So what are they not getting?
...that if you sleep around, even while using condoms, you're going to get infected, especially if you go on drinking binges or use alcohol.
When you look at the academic literature of problematic "sexual risk-taking", the samples in the studies are full of people who have lots of partners, drink a lot, take drugs and who engage in other kinds of dysfunctional behaviour.
You don't get a lot of people who are married, or who stick to one partner long term (even if not married).
The kind of people who are the greatest risk of getting STI's are the kind of people who are not tuned in to responsible behaviour in the first place. They are largely deluded about the risks and consequences of their behaviour, and instead of telling them directly to stop, we engage in the stupid practice of harm reduction, which sends the implicit message that what they're doing isn't so bad: You don't have to stop engaging in anonymous sex in the park, we're just make it safer for you. Don't actually exercise self-control, we know that it's impossible for people to do anyway, especially gays.
As long as we pretend that harm reduction works, that it's all about public health strategies instead of holding people accountable for their dumb choices, this problem will not go away.