To simply say that “X” percent of men have seen one of these sites is the equivalent of comparing someone driving 75 mph in a 70 mph zone with the guy going 120 mph. All sin may be equal in the eyes of God but not all crimes are equal on Earth.
There is a difference between someone that has seen it, maybe even looked a site up and those that go there regularly or someone who did but has stopped. There might even be a few legitimate reasons to have looked at those sites
For example, I was tasked several years ago to create a list of porn sites that would be blocked on a university web site. Thus I have spent hours searching for porn on the internet. I created a document that was about three pages long with the various URLS but I doubt you’d say I habitually view porn.
I spent half a day using a state government computer searching them because a job-seeking client wanted a job in that field. I was not to judge someone’s preference in that regard and when the higher-ups asked me about it I had the client come in and talk to them. Never heard another peep about it.
This is kind of off the topic but why not just use a service like OpenDNS which, with the help of its users, has compiled many thousands of sites with objectional content, keyed by type (i.e. porn, violence, etc.).