The fact that some people exaggerate issues that are sub-clinical into a self-diagnosis doesn't really come into play. The point is determining if trigger warnings are effective and useful for people that do in fact have a clinical issue.
And there's really no need to politicize this. It adds nothing to the conversation and only served to alienate people who might otherwise consider what you say seriously.
Oh but that’s my point, that it’s almost entirely a political issue, not a psychological one. Trigger warnings are used to strengthen victimhood culture, not to shield people from suffering.
As to their effectiveness, unless everything has trigger warnings it’s not going to do much difference, people will still be exposed to the things that traumatise them. I’m not sure that’s a bad thing, you need to get used to living in the world sooner or later.
If you're saying trigger warnings are mostly political (I think ideological is a better label but whichever) that is a different topic. The issue in debate here is wether or not, regardless of any social or political baggage, they have some actual utility. In the case of PTSD or depression w/ suicidal ideation, I think they do. Suicide is, in fact "contagious" in it's way. Letting someone make an informed decision about such content can literally save their life. Similarly, PTSD isn't something really helped by repeated exposure to a "trigger". What you propose in terms exposure to get used to the world is the psychological method known as flooding. It does help with phobias, but generally is not effective treatment for PTSD. Part of the treatment path includes minimizing exposure to known stressors while other treaments have time to take effect.
In short, your ideas here appear to be shaped by your politics, and they simply doesn't match up to mental health best practices for effective treatment.
Most of the "Trigger" warnings I've seen, seem to be there for the benefit of the writer so that they may signal their proper and approved virtue status to potential readers.
Sometimes I see trigger warnings made tongue-in-cheek, as a kind of joke.
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.
And there's really no need to politicize this. It adds nothing to the conversation and only served to alienate people who might otherwise consider what you say seriously.