Porn has been around forever and is documented at least as far back as written history including pictograms.
I agree with most of what has been said. I don't think it's appropriate for very young children although I admit I was interested in my older brother's stash from the time I was eight and it probably did stimulate more than I needed at that age. I also think that the whole sadism, masochism, bondage, and cutting is more than a little too much for me. From my point of view, sex is supposed to feel good. I don't equate being hurt with feeling good and I think that is where it is problematic.
I particularly agree with the comments about desensitization and addictive personality types.
As a person who has been looking at it for more than fifty-five years, I can say that usually, a little goes a long way. A lot becomes boring.