Here's how I see it (and I have no triggers myself so this may be way off):
To me, triggers are like allergies. You are basically allergic and get a reaction when you are confronted with something. It's not voluntary, so you can't really choose not to get the reaction. You can't "toughen up" and not go into anaphylactic shock by sheer force of will. A real, genuine case of PTSD is similar from what I gather.
Allergies is one reason the content of food stuff is usually declared on the package. When there's something that is a not an uncommon allergy that may be fatal, like nuts, it's not unusual to to put a warning label "may contain nuts" on it. I have so far never heard anyone not allergic to nuts be bothered by those labels (but I may simply not have spoken to the right people; maybe there are nut label haters out there too). More unusual allergies aren't broadcasted like that because you can't have warning labels for every ingredient, but people who have them are used to being careful and checking the content listing.
Then there are people who just don't like the taste of something. This ranges from "tastes bad" to "vomit", sometimes because you don't like it and sometimes because you associate it with a prior experience of food poisoning for example. If you mistakenly eat something you can't stand, it's not harmful but may be unpleasant and you'd probably rather avoid it.
Applied to triggers, this would read: a not uncommon, strong trigger is probably rape. Just like nuts, a warning label (trigger warning) seems reasonable. People with more uncommon triggers will probably have to learn to act with caution, because a) you cannot warn against everything because it loses the effect b) you can't predict all triggers c) it places unreasonable onus on the rest of the world. These people are helped by reasonable content declarations though; so insofar it's possible, great idea. This helps the people who just want to avoid certain topics too. It's in everybody's interest since it may make people trust a source more in the future.
So, in general, it's good if everybody lists things that may be problematic, either because some people want to avoid it or because it makes some people ill. No trigger warning should be necessary, just name the ingredient. "Graphic violence", "spiders" or whatever. Or give it an informative title, or whatever other solution fits the situation. Does no one any harm and probably keeps everybody happy. But also, if you really hate something, act with caution. Think before you click or read. You can't put all the responsibility on other people who cannot read your mind.
BUT with some things that are commonly known to trigger a not insignificant number of people and cause them harm (like rape), do like nuts. Put a trigger warning on it, and if you are not allergic, don't read the label. It's not directed at you.
IMO, sometimes meeting each other half ways and being a bit pragmatic isn't such a bad idea compared to grand-standing over the Principle Of The Thing. Even if "warrior" is a lovely, dramatic word (or pejorative if you are so inclined), it's not really a war, is it?