Ao3's tag system is a great tool that helps sensitive readers take more educated risks, but if we're jumping all the way to 'if you don't tag my squick then you are HARMING me' then we've gone waaay too far.
(If OP had just been talking about failing to follow Ao3's rules around the major warnings that would be one thing, but they also threw in 'mpreg or whatever may be their squick' so now it's rant time.)
I do think warning your readers about major common squicks outside the archive warnings is a great impulse! I do it myself! And yet it's also true that literally anything can be a squick or trigger. A potential trigger may seem obvious to you while being totally unnoticeable to the author, and vice versa. Maybe you remembered to tag mpreg, but did you tag for needles? Vomiting? Menstruation? Blood? Doctor's offices? Drug use (because the character takes tylenol one time)? Car crashes? Underage drinking (that isn't considered underage in your country of residence or the time period in which your story is set)? Fatphobia? Character skipping meals? Racial slurs (against Vulcans)? Child endangerment? These are all things that might be reasonably expected to squick or trigger readers because they bring to mind real-world awfulness. I see all of these used as content tags sometimes, but waaaaay less than they 'should' be if authors were truly obligated to protect us from being squicked. And that's not even getting into common narrative or sexual squicks that might be a huge deal to some (unprotected sex, unlubed anal sex, rimming, ass to mouth, breeding kink, daddy kink, undernegotiated D/S, etc) but are so entirely within the realm of normal for others it would never occur to them to tag.
I certainly encourage authors to use tags to help readers find what they're looking for and avoid what they don't want, but enthusiasm for Ao3's tagging system can go too far, wherein readers with specific squicks or triggers begin to hold authors more accountable than they hold themselves. Tagging literally everything is impossible, and there is no fandom consensus on what has to be tagged other than the standard archive warnings.
Creating a new fandom consensus on what MUST be tagged beyond the existing consensus of rape, under-18 sex, graphic violence, and major character death would be incredibly fraught. Standardizing a warning is a powerful normative act, one that can easily inflate existing personal feelings into harsher moral judgments. "We all agree this topic is so upsetting it MUST be warned for" is one step down from declaring a topic entirely taboo. And that has consequences. Victims of rape and child abuse talk about how psychologically damaging it can be to have to cordon off a major part of your own life experiences lest they discomfort others; it can easily feel like you yourself are being declared a blight rather than the harm that was done to you.
Awareness of this impact is why I confess I do find it concerning that the untagged sqicks people get most vocal about tend to involve deviation from sex and gender norms. I understand that pregnancy is a horrifying threat to many fanfic readers and that a lot of us have deep discomfort with our sexual traits, which can naturally lead to us only being able to enjoy a narrower slice of available fictional content, but I never see anybody up in arms about undeniably negative shit like untagged car crashes the way I see some people up in arms about having to occasionally encounter neutral things like untagged mpreg or omegaverse or gender-atypical genitalia.
This is always especially unnerving to me when the offending topic is something that is both inherently morally neutral and entirely possible to encounter among real-life strangers in a positive context. Sure, getting hit with a wave of gender dysphoria when you're trying to read erotica is a bad time, and it's entirely logical to want to select your erotica according to your own genital preferences, but the level of moral outrage people occasionally exhibit when they encounter unexpected genital configurations in erotic fanfic tends to be, uh, pretty unmistakably hostile towards trans bodies, even when it's coming from trans people. Like, okay, say mpreg is a trigger for you because you associate it with threats of corrective rape and you don't want to read about it in your escapist fanficāfair enough. Do you also ask real pregnant trans men in real life to put content warnings on their happy selfies of themselves just existing? Do you get why that would be fucked up? Do you get how it would be extra fucked up to make that request mandatory at an institutional level? Especially if cis pregnancy didn't require any warnings?
Then there's the structural question.
Ao3 content tags were designed to be used positivelyāthe 'exclude' feature did not exist at launchāand as such there was an implied expectation that if you tagged your story as x, you were putting the tag there for people who might want to filter FOR stories with x. That meant a very brief mention of x occurring offscreen wouldn't merit an x tag; nobody came to a fic tagged Arranged Marriage expecting to hear about the main character's cousin having an arranged marriage.
The recent push to use content tags as warnings has led to aggressive overtagging of minor mentions of x, making the x tag less and less useful as a positive filter. This is somewhat mitigated by people using 'minor x' or 'x mention' instead of clogging the 'x' tag (shoutout to people putting background ships in the content tags instead of the ship tags!) which I appreciate. However, this points to a fundamental tension in the practical use of Ao3 tags now that we do have the 'exclude' feature.
If the point is to help readers avoid things, authors will tag very differently than if the point is to help readers find things they might like. And the original structural design of content tags was to help readers find things they might like. Ao3 is firstly for authors to archive their fics and secondarily to help readers find those fics. Only thirdly is it optimized to help readers NOT find fics.
Talking like the 'correct' use of Ao3 tags is to optimize exclusion means you've got your understanding of Ao3 tags backwards.
there is no standardized list of minor archive warnings; squicks/triggers are so varied it would be impossible to mandate warning for all of them
mandating warnings for x inherently imposes a structural & cultural penalty against x content
ao3 is structured to favor positive content tags (help readers find) over warning tags (help readers avoid)
Authors can be expected to tag the stuff they personally find most relevant about their fic, in much the same way a book in the library has a few major keywords attached. More granular content warnings are a bonus. If you as a reader are highly sensitive to encountering a type of content that falls outside of the major archive warnings, you have to take responsibility for that yourself; it will never be reasonable to 100% conclude that a given fic lacks your squick just because your squick isn't tagged. Unless somebody is blatantly lying about archive warnings or actively mis-tagging, they are not tagging their fic 'incorrectly.'
It's great to encourage people to tag more comprehensively! Explaining why certain tags are of interest to readers would be a good start, or perhaps explaining how to maximize the use of filterable tags that work as both positive and negative simultaneously. But OP's post is neither helpful nor accurate.
