Where have you experienced this? I go to some really feminist sites and some really not feminist sites, and while some places tag triggers and some don't, I've never seen an argument about this like you're describing. Either the website cares or they don't. People with PTSD know they can't go anywhere they want and expect to not be triggered, but they might choose to go to sites where they know that common triggers are tagged because they don't want to suffer if they don't have to.

Also, 'most trivial of content' is a misunderstanding of how PTSD works. If you've been violently assaulted after an argument about breakfast and there were eggs burning on the stove while you were nearly killed, then the thought of breakfast and specifically burning eggs might trigger your PTSD. In that case, the person knows that they can't reasonably go out into the world and expect to never encounter eggs or breakfast. That's just an unfortunate part of their reality. However, they might ask their friends to tag their own blog posts with a trigger warning for that content, however inane or 'trivial' it might seem to everyone else, and the friend might oblige because they care about their friend. Maybe that friend would not serve them eggs, either. That's generally how I've observed these things go. It's not like that person is coming into Reddit defaults saying 'HEY SHITLORDS, TAG YOUR FUCKING EGGS,' which is what most of the jokes seem to assume these people are doing, and that they are all for some reason feminists by virtue of simply having triggers at all. Saying "I'm triggered" is parodying the experience of PTSD and the fact that people can be triggered by weird things because that's just how trauma works sometimes, not the discussion around trigger warnings and its loose relationship to feminism.