I assert that the new categories are an objectively good thing. I base this on the fact that they will reduce the chance of harming a few while increasing the freedom of all others. From a strictly utilitarian standpoint, anything which does more good than harm is good.
Those who discuss rights and privileges have all heard or said something like your right to swing your fist ends where my nose begins. This is a statement of a fact which I don't think anyone can disagree with: some rights take priority over others. A major role of government is defining which rights rank above which others, and E2's government is a democracy with editor representatives.
So let's translate that old adage into the terms of the current situation. "Swinging" is "writing." A "fist" is "a graphic or gratuitous description of violence which some might find triggery". And the "nose" is, of course, an affected person's "trigger."
Now, if we can agree that freedom to swing fists is limited by the close proximity of noses, we can agree that giving people a chance to dodge and get their noses out of the way increases the fist-swinger's freedom to flail. Attaching a warning tag to a writeup which has even the slightest chance of triggering someone gives those who expect to be triggered a chance to "dodge" that possibility. Thus, the debate as to whether triggery writeups should be tagged as such without permission of the writeup's author is equivalent to a debate as to whether the fist-swinger should always be allowed to choose whether to punch the space currently occupied by someone's face before giving them a chance to move out of the way. But they don't have the right to indiscriminately punch people in the face, so why should they be given the choice to leave the presence or absence of a nose in that space up to chance?
We should take it as a given that the possibility of triggering susceptible individuals overrides any and all claims of having control over one's own data. That privilege to control ends where it starts to make other people intensely unhappy.
Thus, the discussion we should be having is not "Is it better to allow users to opt out of tagging their triggery writeups with trigger warnings, or to insist that all triggery writeups be tagged?" The only debate where both sides are equally ethical is "Should we try to make sure all triggery writeups are tagged so susceptible individuals can avoid them, or should we delete and forbid triggery writeups altogether?" And in this debate, involuntary tagging is the clear winner, since the latter option constitutes unneeded censorship.
Your limitations on where I can swing my fist should rightfully end where your nose does. Why limit freedoms where they don't come into conflict with more fundamental rights?
Now to address this ridiculous idea that the category tag is censorship or is a slippery slope to censorship. First of all, as I wrote above, it is the only ethical alternative to censorship. It exists in the place of censorship. But let me attack the actual crux of this argument instead of dancing around it.
The fundamental concept in this argument is that authors of E2 writeups should have control of how their content is presented. What a strange world it is where anyone can ever conclude they have control of anything they say after it leaves their lips. The irony is that it is exactly that attitude that leads down the slippery slope to censorship. This site is modeled on the idea that the users have complete control over the writings they publish: they can edit or delete them at will; they retain copyrights over them. However, the infrastructure surrounding the writeups is not intended as a part of that creative work. Nodes, writeuptypes, categories, and softlinks exist to organize that information so that it is convenient to retrieve and relevant to other users' interests. The community as a whole decides how these writings are presented. Otherwise, why would it be up to the other users to promote and demote these writings, or to attach them to categories?
Another viewpoint is that this category is a unilaterally assigned judgment about the works it is used to label. But this is nonsense. The only judgment being exercised is "Is it triggery?" There is no one claiming that triggery works can't be perfectly legitimate and even artistically appealing works.
Lastly, these categories do absolutely nothing to shield the users from questionable content. It merely provides up-front information for those who want to exercise their right to nose around the site without impaling it on any flying fists.
I want to thank Aerobe for taking the initiative for moving this site in a more ethical and just direction. I am not personally one of the "hypothetical" people for whom this addition does the most good, but I call several such people my friends, so it is good to know that people here are keeping their interests at heart too. If the only negative thing that happens as a result of this is that an ignorant and close-minded loudmouth ragequits to return to a life of enjoying privilege without having to notice its existence, then this change has created nothing but benefits for the community.