An important thing to remember in conversations about triggering, which people on the internet, especially redditors, like to refer to as "muh feels", but it's not about feelings or mood largely. Survivors of rape, or assault, or war, or whatever causes PTSD, or various other trauma-induced mental issues, have a serious risk of dissociation wherein, among other problems, a continuity of consciousness is broken. Now if you're reading an article at, say, your office, and you have issues with PTSD from your rape, reading a detailed description of something similar may cause you to dissociate. And this is just one of many issues that could arise, that are simply solved by adding something like "warning: graphic content regarding war trauma". This is something that causes no harm to the writer, or the unaffected people, but means a great deal to a victim, so they have the right to choose to read it or not, or save it for a more appropriate time.
The social stigma stems from the few cases where trigger warnings are essentially used as censorship, shutting down debate. Generally not with things like rape, but by labeling dissenting opinions as "triggering." This is most common in online forums, but I have heard of it happening in college classrooms.
Sure, but I feel like the difference between the two is pretty clear, and I'm not sure if it's fair for the stigma to condemn the entire practice, rather than the specific misuses of it--which is what I personally tend to see, but this might not reflect the total reality.
I would like to say, while I'm generally not too sure how I feel about trigger warnings, that when I had my abortion in college and went around telling my professors what was going on, one English professor proactively looked at the syllabus, told me the next class was going to be about Death and that maybe I would want to miss it. I would have gone and I wouldn't have been triggered by the lecture, but I really needed time, space, peace, and to be with myself at the time. I was so, so greatful he did that for me. To me I guess that is the way a trigger should be dealt with. A student who maybe can't handle something should get a private, considerate "heads up" from the teacher, and the student can then choose to participate or not. If I had triggers I would not want the entire class to know about them, I think it would make it worse.
Of course, this is the goal. It's not necessary that everyone knows who or what is being referred to, but a simple layout of a syllabus would qualify as a trigger warning. It's merely having the availability of information that will be presented in a class, or an article, or a forum, or what have you. People seem to get extremely bent out of shape over... providing what may be encountered, and I honestly can't understand how people equate it with censorship. The topic is still present, the content still there, there's merely a warning going into it. It's not different than network television providing a content warning before graphic imagery. And if you want to get to lower levels even, wherein we're discussing people that have certain phobias or would just rather not see something on, say, their tumblr dash or hubski feed, and you're providing content you know someone will see and would rather not, providing something as simple as a tag saying "spiders" puts you out none and provides a benefit for someone. Of course this isn't such a large matter if you forget as it would be if we're talking about potential trauma. I see plenty of people complain about triggers existing and being shamed for not including them, but I've yet to actually see someone call out another for not including triggers unless it was a serious matter. Mostly everyone complaining about having to provide a content warning is completely oblivious to the effects of trauma.