The whole proship/antiship debacle is a deeply unserious mess of a "debate" that's stemming from deeply bad-faith assumptions on both sides, a slurry of ad hominem accusations flying back and forth, and a massively disproportionate sense of scale. I have friends who are proship, and I have friends who are antiship. As a rule, I'm not friends with pedophiles, nor am I friends with reactionary puritans. So let's just nip both of those accusations in the bud right now. I think both groups have some points that are valid, and some points that are invalid. But overall, I think the whole thing is a little silly and a lot of people are getting very heated about very little. I'm going to do my best to parse out good-faith readings of both sides in this debate. I know that the middle ground fallacy is a thing, but I genuinely have seen good points from both. I'll start with antis, then go on to proshippers.
The anti position seems to be as follows:
We know that fiction has an effect on reality. Fiction reflects the real world, and representation has an impact on people. So, it logically follows that fictional works with bigoted or negative elements can be bad for society. Like, to give an example in extremis, the Turner Diaries are a vile piece of neo-Nazi writing that have directly inspired mass shootings and bombings, and are still a core piece of QAnon philosophy. So, the anti logic goes, works like that should not be platformed. And to home in on more common examples, antis have long been critical towards AO3 for its lax content moderation policy, as it explicitly allows works containing depictions of racism, transphobia, and pedophilia. If fiction impacts reality, which we do know to be true to some extent, then it follows that fictional works containing "problematic" elements (I hate that word, personally, it's extremely vague) shouldn't be hosted on any given platform.
That's the good-faith anti position. I'm being charitable here, and not including the self-proclaimed antis who declare that proshippers are groomers or pedos. In the same vein, I will not include self-proclaimed proshippers who declare that antis are cultists or puritans.
The proship position seems to be thus:
While fiction does impact reality, it tends to reflect existing views, rather than directly influence people. Furthermore, the artist's intention in creating art does matter; works discussing racism will contain examples of racism. To reuse the example in extremis, the Turner Diaries are vile, but nobody became a neo-Nazi by reading the Turner Diaries who didn't already hold fascistic tendencies. Game of Thrones aired on TV for years, and it had no effect on public attitudes towards incest. To home in on AO3 again, proshippers hold that AO3's purpose is to serve as an archive of fanworks, good and bad, and that there are plenty of legitimate reasons to archive works with harmful ideas - occasionally, when studying harmful ideas, you need to be able to cite harmful works. Proshippers also hold that harmful views in fiction do not correlate directly to authors or readers holding those views, and that readers and authors have the right to read and write whatever they want, with the understanding that they possess critical thinking skills. (Additionally, there is a concern about censorship on any site that hosts queer media - we have historical examples of sites like LJ and FF dot net purging queer media under the guise of removing harmful media. Just look at the alt-right calling trans people "groomers".)
So, those are the good-faith arguments on both sides, as far as I can parse them. And if it seems like the proship arguments are all rebuttals to antiship arguments, that's because they are. "Proship" as an identity formed in reaction to antiship talking points. Nestled in there are debates about whether fiction can be harmful to real people, about who should control what fiction is allowed, and what an author's responsibility is to society. All of these are real, important questions, which is why it sucks that this discourse quickly turns into mudslinging, harassment, and potentially libellous accusations of very serious real-world crimes in response to opinions on media.
At its core, the antiship position is about keeping people safe - especially children, given its focusing in on works depicting pedophilia.
At its core, the proship position is about resisting censorship - especially censorship that can and has lead to queerphobia.
Both positions have valid points, and both have deeply unserious claims that take the most extreme cases of the opposing side and paint them as representative of that side. Both have led to severe harassment and abuse.