> Heck, I don't have PTSD but I don't particularly like seeing sexual violence in movies or television shows and more than once I wish I had been warned about it ahead of time.

Related to that, a lot of people prefer watching certain genres such as action, romance, sports, sci-fi, comedy, etc... If it's ok to inform people they're about to watch an Adam Sandler romcom then I don't see what's so bad about informing people they're about to encounter triggering content.