SL: If even one person in the whole world reconsidered watching one movie, or refrained only one time from doing only one tiny sin, based on the generic comments – while everyone else reading it was angry at the rebuke, then not only was it halachicly correct but it is furthermore a total success that was well worth it.
And, indeed, I think it is fair to say that it is possible that someone, somewhere, someplace, at some time now or in the future reading this thread will reconsider their habit of watching sinful movies. Maybe just once. Maybe for a lifetime. Maybe this week. Maybe in a year from now. Maybe just once. Maybe permanently.
And since that is even a possibility of happening – once – even though it may never happen that someone reconsiders, since it is possible, that alone means that it is not only halachicly correct to give the rebuke but, rather, it is halachicly mandatory to give it.
Though, imho, I think it is likely to have a beneficial effect on at least someone, at least once.
I say so with the authority of having had more than one confirmed success in this arena.