In the case of France, for anyone who understands French, in this debate[1], it is said that when men watch pornography, their brain gets used to a certain category of female bodies to whom their wife/girlfriend does not resemble, hence they lose attraction towards their partner, but also in the women around them and the ones they see in their daily life, in a nightclub ...etc.
It is also said that porn is more and more violent, so lots of men are not excited in the normal and romantic way of making love (most likely your wife/girlfriend won't let you treat her the way your brain is trained to through porn)
There is also one interesting opinion in that debate (from an author which was not present, but was quoted): when French boys get a bunch of sexual experiences in their adolescence, it is normal they loose that sense of romance and attraction once adult.