It's very hard to find good studies that highlight the beneficence of pornography because there exists a great body of misinformation as created by political groups (of course with religio-conservative inspiration). Case in point, the Meese Commission and it's body of non-experts that only solicited information from groups and individuals that would parrot the traditional sentiments about sex that have survived in word and spirit from the Victorian age. Essentially, the idea that exposure to sex leads to criminal sexual acts.
However, with little bit of elbow grease and Google, you'll be able to find numerous reports, peer-reviewed and fairly recent, that present evidence completely contrary to the fallacious conclusions of the aforementioned committee (and many others like it). The common thread of this recent research is that an increased availability of graphic materials carries an inverse relationship with the amount of sexual crimes. Simply put: more porn, less rape. Whether this is through the demystification of sex, or the exorcism of sexual frustration using visual aid, or something different altogether, that's for further research.
And of course, blaming a failing marriage on pornography is pretty dumb. I'm afraid the crux of the problem is much deeper than finding a scapegoat: it lies in the arrangement and expectations of marriage itself.
Men are biologically capable of reproduction well into mid-life and even old age, while women have a relatively limited span of time to reproduce. This falls in line with the proposed distinctive reproductive strategies of men and women. Men sort of spray their genetic material all over the place, both metaphorically when choosing mates and literally when fucking them. It's a quantity thing for guys. On the other hand, women are all about quality. They have to be because of their limited capability for reproduction caused by their limited period of fertility and the amount of time it takes to have a child.
With that little bit of evolution out of the way, you can see why a 40-something year old male will have the propensity to view pornography. He's whacking it to all the 18-something teens that stimulate his primeval, evolutionary proclivities. Combined with the fact that his wife is dried up (sorry ladies), this may lead to infidelity, a ruined marriage, or at the very least, some very hurt feelings.
If a couple were to be more liberal and comprehended these ideas, they would come to the conclusion that sex is not love and they can be mutually exclusive. Though, this would undermine the traditional institution of marriage, and as such religio-conservatives can't fathom the idea (until, of course, they're holding a press release to apologize to their family and constituents for their recent, torrid affair).
