Edvard stated: source post
Then you can end up desensitized to sexual stuff you'd be exposed to in real life, end up with some weird fantasies and fetishes which only they can turn you on. And when a woman is naked next to you you can only get excitement and pleasure if you picture some tentacle anime or large insertions or fuck knows what.
You are correct; it can cause desensitization. Which I imagine you would view as "unhealthy." I remember Rass and I arguing with you that a lack of interest in having sex is not unhealthy. I believe your viewpoint was that sex is a biologically natural urge, and therefor lack of that urge is a sign of something amiss. Rass and I contended that people can view the act differently. And that just because something is a biological norm, does mean it is "correct," or "true."
I remember in middle and high school, the girls I were most attracted to, I did not view as objects of lust. Not because I thought, "oh no, she won't be into some kinky shit." I thought that way because I had an idealism (however naive) of purity at the time. This caused some problems relating to going on dates in high school. These girls had raging hormones, and after a few—usually about 3—times spent together with romantic overtones, they would subtly imply they wanted to fuck. But that just seemed like bizarre to me. Girls who I never spent time alone with outside of school soliciting me for sex seemed even more bizarre. The thing was, I wasn't looking for sex. I was looking for something with a bit more depth. I never considered their behavior "wrong," but that's just how I viewed things.
That aside, I don't claim to be asexual. By 16 I was no longer a virgin, and I've had sex sporadically throughout my life. Maybe for some people, porn does make it so that they need to "up the ante." All the sex I've had, spare one time, has been vanilla though. Sure, I have fetishes, but I don't feel a burning need to indulge in them. I'm more interested in chemistry than specific fetishes, and if there is no chemistry, I am not interested. I've had one-night stands with people I'd just met that night. And they mostly sucked, because the whole ordeal to me felt forced by need.
Is this all caused by beginning to view porn at a young age? Maybe. Has watching porn over the years shrunken my striatum? Possibly so, as the study the OP posted would imply. But I'm not even a "porn addict." I actually have to masturbate, because if I don't, after a while I will literally start blowing loads at random.
Do I feel sexual arousal in normal interpersonal situations? Sure. It's just that this arousal is overridden by my interest in chemistry. But I don't feel the need to force this chemistry to exist. It seems unimportant to me, and I don't see why I should feel any way otherwise.