I think there are various problems with porn. Firstly, I don't know what the current culture and atmosphere is like in adult industry, but there are arguments against porn because it enabled and funds the exploitation of women. I don't think this is true for all adult productions, but it's a difficult matter to breach, as the relationship between porn and its consumers is very tentative and often anonymised.
The other main problem is the potential effect on consumers of porn. I don't think porn is solely the cause for distorting people's perspective on sexuality, but the absence of other sources of information- especially given parents unwillingness to educate their children, or allow schools to educate them, in the name of preserving their innocence- can cause porn to be the sole source of sexual education. It's much less surprising that, without the contextual understanding that porn is idealised and targeted to be as entertaining as possible, that some may develop unhealthy sexual attitudes because of porn. Much in the same way you get some kids that are brought up on wrestling and are inappropriately rough.
On the other hand, porn can be quite diverse and to anyone adventurous enough, it can actually be quite enabling to help discover alternate forms of sexuality and many of the interesting and varied niches that exist. I suspect it's far more common for porn to act as a gateway to self-discovery rather than a primer on sexist, self-centric sexual behaviour.