I like the term. When you think of porn, you think of something that is excessive.
Porn - television shows, articles, photographs, etc., thought to create or satisfy an excessive desire for something, especially something luxurious: the irresistible appeal of food porn; an addiction to real-estate porn.
Torture porn to me perfectly connotes the idea of excessive torture with lots of blood. I am a big fan of horror movies, but I really don't care for movies where people are just tortured and murdered in gross ways. Some fans watch horror movies for the kills only and I think it is that narrow hunger that some of these horror films plan to fill. The horror is mainly built around the body being tortured.
If I call a movie, "toture porn" - for me, it is a diss to a certain kind of horror film. I guess how offensive it is to you depends on how much you like those kind of horror movies.
While there has been bloody movies since forever - I feel like a lot of them looked fake and that was part of the fun. Movies now make the gore so realistic that it's not very fun.