For starters, make sure nobody under 18 can watch porn and figure out regulations that hold the companies accountable. If a 13 year old can be kept from online gambling, they can be kept from online porn. It doesn't have to be 100% effective, just start trying. It shouldn't be that hard to make a lot of improvement. I'm actually sort of disturbed that this hasn't already happened and that the current state of things isn't seen as a problem.
The answer to these type of questions is almost always let it run its course and in a few generations the gene pool will change to favor people where this is steadily less and less a problem. It is important to note that that is not the correct answer because it is a good answer, it is the correct answer because the alternatives are draconian and terrible to the point of being worse.