No one climaxes unexpectedly from watching online porn. You decide you’re done. The first 10 minutes are thrilling but after that you’re not holding back from orgasming; in fact, you’re trying to remind your penis to stay hard until you find whatever it is you think you’re looking for, because you think you’re going to want to suddenly come when you find it, whatever it is will be so awesome you won’t be able to hold back— but it’s never so spontaneous. You have to decide the time has run out. This is why online porn is so problematic: there’s no natural end in sight.
And for most, the biggest problem is the drive: you don’t do it because you’re horny, you do it because you’re bored. With porn that available, you never get to really horny anyway in the same way Americans never get to really hungry.
In other words, online porn isn’t a drug, it isn’t an addiction, it isn’t a sign of deviancy or a trigger for disease: porn is junk food. It is a bag of potato chips you eat when you aren’t even hungry, and once you start and the initial “mmmm!” passes you’re all in, may as well finish the bag, you’ve ruined your diet/night already, start over clean tomorrow.