It’s not really your job to convince your friend of this. But I would mention how degrading it is to the people in the video. I think it was St. John Paul the Second who said “The problem with pornography isn’t that it shows too much of the person, but that it shows too little.”
Turning people worthy of heaven, created in the image of God, into images to be gawked at for fleeting pleasure is wrong. Many women in prob videos have very rough lives. Doing horrible, degrading work because they have nowhere else to turn. Even if I considered it moral I wouldn’t support such an exploitive industry.
Many men, even nonreligious men, have noticed the harmful effects of porn on them. This might included erectile disfunction, unreasonable relationship expectations, no longer finding real women attractive. Not to mention all the more subtle, and in my opinion more dangerous effects: watching porn will change your attitudes toward women, especially young men who start using porn before having relationships. As well as worsening or causing sexually deviant interests. Training your brain to always expect something new isn’t good. Especially if your friend ever plans on commiting himself to one woman. (And admittedly many nonreligious men have no intention of doing so).
Note: I slipped into assuming your friend is a man. If not almost all of this applies anyway. Please excuse my assumption. Women do struggle with porn as well and deserve to know they’re not alone. I just don’t want to retype it all.