There’s quite a difference between the popularized image of what trigger warnings are and the common sense use-cases like “this media contains depictions of graphic sexual assault that some viewers may find disturbing”.
traumatic events are not a normal part of life and fortunately most people are never forced to experience something truly traumatic. Uncontrolled exposure does not build up "immunity" or help individuals work through or process the trauma. if the warnings seem unnecessary to you, then they're probably not for you.
Put 'scientific support for trigger warnings' in your favorite search engine and you'll find meta-analysis, RCTs, other types of studies, reviews, as well as discussions from the APS, other psychology and psychiatry related publications, etc.
This isn't to say removing trigger warnings is a replacement for actual guided therapy, exposure therapy or otherwise, but it doesn't seem like it would be a negative outcome for long term mental health and would be a benefit for anticipatory distress and potentially in combating avoidant behaviors (though not all studies universally found them to increase avoidant behaviors - just some)
This is a separate question than when it comes to general polite society and social expectations and what is and isn't considered a courtesy. The studies also aren't dealing with people that have just gone through the traumatic experience, so you could make a reasonable argument that exposure to something still fresh could have a very different impact.
There has been no proper research on the effectiveness of "being given a trigger warning, and then not consuming the content because of it." Which seems to be the most important factor to consider when it's about avoid sudden panic responses.
Well, there has been. From multiple angles. One, avoiding content because it might trigger you is just... avoidant behavior. Which is pretty much universally considered a bad thing. There's a big difference from seeking out exposure because you want to do your own exposure therapy (bad thing) and just letting yourself be exposed to things in a more organic fashion (good thing).
Two, most research indicates that TW do not actually reduce the consumption of content. Not all of the studies are on "did they help people process content they watched," as a lot of them are "did the TW make people not watch the content to begin with." Mostly it seems to haven no impact. A smaller subset of studies showed effects in other directions - both reduction and increase of content viewing after TW. If they reduce viewing I'd argue this is bad because it's avoidant behavior, and I suspect that the 'forbidden fruit' effect is also not positive because it's now giving you pre-viewing anxiety and is no longer the more organic 'let exposure happen naturally, don't just stop watching the news because it might contain stories about war.'
I think they are. Normal people can't stand emotions, these warnings keep them comfortable.
