Sanity...Of course we can never stop people having sex, people will do it anyway whether it be harmful or not.
Incest is criminalised on health and social grounds, even if the people concerned agree to be sterilised so that no offspring are involved.

But... we can ensure that the transmission of STDs amongst the demographic most massively affected, is slowed or halted by frequent testing and contact tracing as recommended by all health agencies....
As I said earlier, how the agencies enforce their suggestions is up to them, but if infection rates amongst MSM continue to rise by 10% annually while rates in all other demographics are falling, action to encourage responsible conduct in the MSM demographic will have to be taken.