[Content note: rape is used briefly as an example]
Trigger warnings are basically an accommodations issue. Some people with PTSD are triggered by certain topics, to the extent that it causes them panic attacks, dissociation, or some other form of reduced psychological functioning. So we take reasonable steps to accommodate such people, such as warning them of topics to come. Depending on the person with the trigger, they may react by avoiding the discussion, or simply by proceeding with greater mental preparation.
Trigger warnings are mainly discussed in two different contexts. First, on the internet, such as in a blog post. Second, in the classroom. The latter context especially seems to attract a lot of media coverage, with people arguing over the censorship of literature.
Trigger warnings, though, are not at all like censorship. Attaching a trigger warning to a book doesn't mean hiding it from view, it just means attaching a warning. Sometimes people also call for the removal of a piece of literature from the curriculum because they find it triggering, but that's a different kind of accommodation entirely. It's not always reasonable to change a course curriculum to accommodate a few students, but trigger warnings are almost always reasonable.
The only thing that might make trigger warnings unreasonable is that people are triggered by a very diverse set of things. Supposedly, the most common trigger warnings are for things like sexual assault and rape, which makes sense since those are common sources of trauma. But in general people can be triggered by rather ordinary topics, and you really can't anticipate everyone's triggers on the internet. And if we could anticipate everyone's triggers, the number of trigger warnings required might be unwieldy.
We may just have to settle for the fact that whatever we talk about might cause some harm to some individual out there who is listening. This is not very satisfactory to people who insist on social justice perfection, but it's the way it is. It's not a tremendous moral failing if someone fails to add the correct trigger warnings, it's just a bad thing that happens sometimes. Sometimes the best thing we can do is allow people to excuse themselves from a conversation at any time. That is also the polite thing to do in general.
We also need to talk about how trigger warnings are used even by people who do not have triggers. To give an example, I do not suffer from trauma, but I still appreciate trigger warnings for sexual assault when people care to add them. Sometimes I encounter some media which implies sexual assault, taking me by surprise, and my reaction is "oof, heavy topic". Warnings have very marginal value for me, but I appreciate them. It's sort of like subtitles in movies, which I generally like even if I don't need them.
I generally prefer to call trigger warnings "content notes" or "content warnings", because I'm agnostic about whether people use them for triggers or for something else entirely.
It's fine and good for people without triggers to make use of trigger warnings, but there seem to be a few distortive side effects.
For example, trigger warnings on sexual assault and rape are often used for the political goal of keeping the issue of rape in the public consciousness. That's a political goal I can get behind, but it also makes me unsure whether the most common trigger warnings accurately reflect the most common triggers. I've heard, for instance, that people with trauma like specificity in their trigger warnings, but since you don't need much specificity to raise consciousness, this doesn't get talked about much. I've also heard that discussion of dieting is a common trigger for people with eating disorders, but it's certainly not a common trigger warning. There's a lot of ignorance of the most common triggers, and I include myself in that ignorance.
In other cases, trigger warnings are used to label things that are "bad". In principle, whether something deserves a trigger warning has nothing to do with whether its content is "bad". Even if I have the most enlightening discussion of what rape victims go through and how to support them, it could still be triggering to some people. On the other hand maybe fewer people would find that triggering, I don't know.
Speaking more to my personal experience, there are a lot of discussions of rape and sexual assault that I don't like for their content. I don't like victim blaming. I don't like when people are so blasé about it, as if they forgot that it actually happens to people. I particularly dislike stereotypes of rape as something perpetuated mostly by violent strangers who slip you GHB and Viagra.
But these are objections to the message. Objecting to the lack of trigger warning is not an objection to the message, it's an objection to the medium. It's a common for people to object to the medium as a sneaky way of taking down a message they don't like, but I do not think trigger warnings should be used this way. After all, a proper use of a trigger warning doesn't involve taking down the message at all.
Lastly, I acknowledge that there is a large crowd on the internet who mocks trigger warnings as if they are inherently ridiculous. I have an argument for why these people are harmful and wrong, but tragically it does not fit in the margins of this blog post.