Good, let's stop using them and go back to talking about bad things like adults who have a reasonable grip on their feelings.
For example, functional adults don't discuss topics like rape unless they are reasonably certain that discussion participants do not have an associated traumatic experience.
The purpose of trigger warnings is to let people excuse themselves if you do not have that familiarity or certainty with your audience, e.g. a classroom setting.
I'd argue that not using trigger warnings for such topics with unfamiliar people is immature and callous.
The problem is that we have an epidemic of people who are triggered by normal words and even the mention of important topics -- like rape, murder, wars, etc -- that ordinary people do need to talk about, so when your sensitivity expands so much as to infringe on the ability of healthy adults to discuss the issues of their day, that's when it's no longer the case that adults can avoid discussing any topic that might upset the fragile minority.
Isn't that the point of a warning? You're still going to discuss it, just with a warning up front. If you were going to avoid discussing it, you wouldn't need a warning.
What we are talking about (supposedly) is content that is necessary to be in the lecture. It's necessary for the students to learn it. So do the trigger warnings help or not?
A good example here -- since this often comes up in the context of Universities -- is rape, and specifically rape law[1]. You have a situation where university professors are afraid of covering rape law because it might terrify their law students[2]. From the New Yorker article written by Harvard Law Professor Jeannie Suk Gersen:
"Student organizations representing women’s interests now routinely advise students that they should not feel pressured to attend or participate in class sessions that focus on the law of sexual violence, and which might therefore be traumatic. These organizations also ask criminal-law teachers to warn their classes that the rape-law unit might “trigger” traumatic memories. Individual students often ask teachers not to include the law of rape on exams for fear that the material would cause them to perform less well. One teacher I know was recently asked by a student not to use the word “violate” in class—as in “Does this conduct violate the law?”—because the word was triggering. Some students have even suggested that rape law should not be taught because of its potential to cause distress."
So when talking about this issue of "being sensitive" it matters a great deal whether the request is a reasonable one to remove unnecessary material or whether the request is unreasonable. It's not just a question of being considerate without taking into account the reasonableness of the request.
Now there is nothing wrong with being upset at things -- I don't like the sight of blood. But I would never try to be a surgeon, nor would I complain in medical school that the sight of blood traumatized me. Someone with a fear of heights can't go to Pilot school. If I went to medical school, it would be my responsibility to know what I was getting into, just as someone going to law school is responsible for knowing what they are getting into. Otherwise, don't enroll.
This reminds me of the beautiful Rumpole novels by Sir John Mortimer, where the main character is employed as a defense attorney but all his partners are bothered by so many criminals visiting their offices. I mean, there is a line between "please don't joke about polish people" to "please don't mention rape in this law school", and the pro-trigger-warning movement has crossed this line. They cannot reasonably expect to be shielded from these topics in lectures, this material will be on the tests and they need to learn it, and the secondary backup attempt of giving them "trigger warnings" to psychologically prepare them for the trauma has been shown to not work.
[1] https://www.insidehighered.com/news/2014/12/17/harvard-law-p...
[2] https://www.newyorker.com/news/news-desk/trouble-teaching-ra...
Even if it's true that trigger warnings do not help people who go on to read the material, and even if it's true that reading the material is generally a good way to manage one's PTSD, I still think the students should be able to make their own informed decision about what they want to do. If they would rather avoid upsetting material, that's a decision they should be able to make. The only one they might be hurting is themselves.
OF COURSE someone who wants to be a surgeon shouldn't be if they can't handle the sight of blood. Nobody is arguing otherwise.
To use Jeannie Suk Gerson's conclusion as a stand-in for your argument:
> Instead, though, many students and teachers appear to be absorbing a cultural signal that real and challenging discussion of sexual misconduct is too risky to undertake—and that the risk is of a traumatic injury analogous to sexual assault itself
That is one (relatively qualified) person's opinion, and I don't think she polled the students and teachers regarding the subject before writing this. I would remind that she is a professor of law, not of psychology. She may be misunderstanding the situation. She certainly writes extremely often about the problem despite being a law professor. At best, its a hearsay criticism and take it as you will.