Also, it's gone beyond it's originally intended purposed and begun to be used with any sort of "extreme" content, e.g., horror/gore/jump scare videos etc, where it serves as an inducement to watching, not a warning against it.

But aside from these, in the original intended context, I don't really see the behavior you mention. Maybe it's the case that a small minority are the caricatured smug virtue signaler you portray, but if so you are painting their entire use with the brush of an extreme minority of an example.

Visit a depression support group forum. You'll see just about any post with suicide content with a trigger warning. Why? Because while it's a common issue among the depressed, suicide is also contagious in a way. People already at some risk are much more likely to attempt or succeed when exposed to content of that nature. It's not uncommon for there to be a slight uptick in suicides after a public figure commits suicide. The second of two suicides within a week from survivors of the Parkland shooting may very well have been influenced in this way, as might the third suicide of parent of a Sandy Hook victim that committed suicide a few days after that.