Porn is exposure to other possibilities. Its not surprising that it can lead to negative things in a marriage, after all, you don't know what you are missing if you didn't know it was there to start with.

I had a 45 year old friend who's wife recently left him, he started dating again and had NO idea that women actually did things like enjoy sex or shave their pubic hair. I know he doesn't watch porn ;)

My wife and I started watching porn together, and it opened our eyes to what more we could have sexually and eventually helped lead us to swinging, and also helped my wife realize she was bisexual.

We no longer watch porn together, but sometimes our lives are basically a porn. Its been a very positive thing for us (and we've been together for 20 years).

Porn is neither good nor evil, it can destroy a marriage, or it can even enhance one. While we took it to swinging I know of couples who just use it to spice up their own bedroom.

I think the real issue is when porn is a "one sided" thing. When one partner (usually the man) does it in secret, hiding it from a jealous wife. Marriage is a together thing, and when porn is used as a together thing the outcome will be far less negative, and perhaps positive.