Porn is an entertainment. But with a difference.
When a man sees any movie he doesn't get carried away and doesn't think he has taken part in it. Porn makes one feel the sex. Its effects are visual and auditory and it makes the mind think that the body is making the moves. Thus it prepares the body for sex, causing erection, releasing pre cum and even ejaculation. This is because it caters to the basic instinct of man like a hunger being satisfied.This effect of seeing porn is due to release of some chemicals in brain which signal "pleasure".
When a man watches porn he also tends to binge on it, and the person seeing porn slowly goes from one scene to another and the chemicals released in his brain saturate the various receptors. Slowly after a while, the man does not get aroused by what he saw, and he tends to hunt for more exotic variety of porn, thus his adaptation to porn takes place.
To beat this he tries to go for more aggressive type of porn with multiple partners, gang bangs, rapes, pissing, fisting, leather , and other fetishes. These excite him as his mind is used to normal porn and these exotic things tend to release the pleasure chemical.
Thus the man unknowingly sets up a high bar for his stimulation. A person who was satisfied bys eeing just few basic scenes, now gets an erection ONLY after seeing the deviant, fetish porn.
The person hooked to porn has poor inter human interaction. He does not like to mingle with friends. His whole world is occupied by thoughts of sex and its procurement. He stops using his fantasy to get a sexual feelings. He uses porn to get aroused. This type of person then fails to get erections and sees himself as suffering from Erectile dysfunction. This loss of erection is more due to high stimulation bar set by the man for himself. He appears secretive, does not like normal sex with his partner. This drives him to have sex less life which can be relieved only by exotic porn
This makes things worse in his real life.
Hence porn is a double edged sword.
Excess consumption is nowadays more due to available of free wifi and whatsapp group sharing where free porn is distributed to friends, and the 3G, 4G connections download these into the phones unknowingly. Once a porn is there, the person will surely see it. This starts the porn addiction.