There is a lot of data to corroborate these ideas. There are many porn consumers who have recognized their addictions, even if they are not actively battling them. You can learn about these things by looking for them. http://obscenitycrimes.org/cline_unabridged.pdf is a 23-page (unfortunately magazine-like) overview of the research of one sex therapist; I couldn't find something more clinical in the brief time I was able to look.
Regarding the default tendency, there are many things that humans naturally prefer that are much, much worse than the alternatives. There is a default inclination toward drugs and other seriously harmful solutions, but that doesn't make heroin good, does it? Our attraction to these things is a very complex issue which I'm not fit to explain scientifically. That doesn't mean it's not real.