It's not important what other people think of porn in relation to the OP's situation, she is upset and that's all that matters, along with how she and her partner deal with things.
I think that porn can be benign when it's used by couples with emotional maturity who are open with the fact that it's used to enhance their sexual experience, alone or together.
Porn use is not a part of my marriage but if people tell me that they enjoy it and it has a positive impact on their sex life then who am I to argue? Some people genuinely don't care about the ethics of the subject, in the same way they don't care how food or clothing is produced ( maybe they should but that's a different matter ).
The bottom line is , her husband should take her concerns seriously and put them above his like of porn - if he can't do that and thinks she's being stupid, it's pretty selfish behaviour.
I have to say, if I ever thought my husband was looking at 18 year olds I would be horrified, I hate the thought of men with daughters looking at women young enough to be their daughter, I find it absolutely sickening in fact.
It's a shame there are no men on here who can explain precisely what it is that they get from porn, that they can't get from their imagination. I genuinely don't understand why they need something to look at in order to masturbate?
I do honestly wish that something could be done about the proliferation of internet porn though, teenage boys are always going to seek it out and will get an extremely warped view of what love and sex are about.
There's no doubt that porn use ( and the secrecy that can surround it) is severely damaging some relationships.
I think that men should certainly be a lot more thoughtful about porn, perhaps if they considered how they would feel if men were viewing theirdaughter in that way, it wouldn't be such an attractive prospect?