From what I've read, long-term compulsive stimulation from porn is proven to alter the brain chemistry in a way that makes it difficult for the consumer of such materials to be able to maintain real, healthy relationships. Of course the addicts themselves and those that promote the industry as "harmless" would shill for it.

There's a definite danger to opening the floodgates on one's self. Not to mention the fact that it's also used as a form of escapism for people instead of addressing the problems that may be surrounding them in their life. Easier to jerk off to a video instead of focusing on and addressing the issues between you and your significant other, or watching porn all day instead of developing healthy social skills. See also: the average Redditor.

What's worse is advancements in technology have enabled a universe of ready-to-reach sexual content. So even more than ever today, porn is a major problem because of accessibility and the sheer volume of content available to the youngest of age who can reach the internet. These ain't the days of Playboy mags and Hustler tapes where you were considered "lucky" as a kid if you stumbled across.