is it just me or are people afraid of writing and drawing nsfw zutara? for a ship that’s supposedly a self insert porn garbage there really isn’t that much explicit material with them
There is definitely a group of zutara shippers who are afraid of it.
I have not forgotten the zutara smut week discourse and how certain people who turned out to be radfems tried to drag me into it. This is also what started that confession blog, which doesn't even pretend anymore to not be blatantly anti zutara.
I do think some of this is caused by, as you say, zutara's reputation as dark and edgy. Which is not to say that zutara isn't or can't be a wholesome ship on its own! Not everyone who writes fluff is afraid of darker or edgier stuff, and zutara as a whole is one of the most idealistic, softest versions of the enemies to lovers trope, so it makes sense that most of the fic is that way.
But yeah, there are some people who try to police other fans because they are afraid of the antis' labels. Which to me is ridiculous because it's only giving credibility to those labels.
Specifically, policing sexual content in particular with THIS ship is often masked as progressive or anti-racist, but is often highly misogynistic and racist itself.
I've seen arguments that writing zutara smut somehow promotes this idea of Katara in particular (because it always goes back to the woman, naturally) as oversexed, or writing certain types of sexual dynamics is misogynistic (your capture fantasies, for example).
But that only gives credulity to the idea that what kind of sex you have, or how much of it you have, or who with, is a reflection of virtue or morality in the first place. Like, the idea that Katara is being oppressed by a man if she chooses to have sex with that man is bonkers, backwards, and not particularly progressive. Which is not to say that sex by itself is inherently progressive, but it's not inherently oppressive, either, and that thinking can only be traced back to conservativism and misogyny.
The anti idea that having a romantic (or god forbid, sexual) relationship ruins Zuko and Katara's friendship also comes from a highly anti-sex, misogynistic place that pretends to be progressive. See the jokes Bryke made that follow tropes about women being attracted to "bad boys." In the famous video they made mocking shippers, they presented Zuko and Katara as people who weren't even friends, who have nothing to talk about or do together other than making out, despite them actually building a strong friendship in the show itself. So this fear of (particularly women's) sexuality is not even appreciating the friendship aspect, either.
Now that we have the movie, I've seen a resurgence in cheating headcanons, but also a resurgence of the hand-wringing about how Katara and Zuko are "too good" to cheat. But if Bryke wants to act like Katara's virtue is tied to her faithfulness to Aang, why should I adhere to some pretense of moral virtue? You can't put a woman into a little box and then blame her for stepping outside of that box.
I do think zutara is a healthy and wholesome dynamic, but also sometimes I just want them to fuck nasty, and no, I'm not going to apologize for that.