After some thought, I'll give some context and depth here that the original article lacks. To begin with, I'm just going to use romanized versions of some terms from the article: ロリコン and 児童ポルノ to be specific, the former of which people tend to romanize as 'lolicon' (you may recognize that this is a shorthand for 'lolita complex') and the latter which I've never seen used, but we can call 'child pornography' as the author notes.

The concerns of operators regarding federation and explicit content are actually quite significant in regards to lolicon content. If you live in Canada you don't want to be anywhere near it. There are (likely apocryphal) stories that bounce around between colleagues and friends of mine about people who were unfortunate enough to import a sex toy or anime product that had a risque piece of lolicon art on the packaging. Customs and law enforcement in Canada happen not to be particularly interested in the fine details of what is or isn't obscene, so you can end up doing some jail time or (if you're lucky) deported. This applies to other sorts of content as well. Canada is hardly the only country where you could get in trouble, it just seems to surprise people to find out that they have an aggressive stance on this compared to (for example) the United States.

I mentioned "other sorts of content". Like what? Well, for example, there is a directly related concept referred to as 'shotacon', and it will also appear frequently on pixiv and other websites - not to mention on anime-focused websites like 4chan and reddit. You can treat this term as a direct equivalent to lolicon, except instead of girls it features boys. Oh, right. So since the author originally neglected to explain this, a brief summary of these two terms:

Lolicon roughly describes a genre of works depicting prepubescent girls, or girls who appear to be prepubescent. Typically it is not explicitly sexual but it often has very sexual undertones, framing, or at the very least the subtext is sexual. It typically involves older men (say, high schoolers or college students) if not extremely older men. Sometimes it involves older women instead (this is basically a subgenre, with terms for it like 'oneeloli').

All of this is extremely complicated, especially if your only interest is in figuring out what the heck is going on. If presented with some of this content it can be difficult to figure out why someone might find it obscene, or why someone might NOT find it obscene. Content that is inoffensive if viewed without context can become very distressing if you learn that it's placed in a highly sexualized context.

If you are a translator, or animator, or moderator, or any other sort of creative working in comics, animation or video games, you will probably run across all of this. It tends to create a fuss any time this content shows up in storefronts - Valve's Steam storefront has had lots of issues with explicit lolicon content appearing in games for sale.

To return to what I brought up above, so there's a related genre called shotacon. All of the above description for lolicon applies - people draw art and animated content and make video games for these genres and subgenres. The distinction is that shotacon is about prepubescent boys, not girls, and this distinction is surprisingly important when it comes to people's determinations about whether content is obscene. It's even important in Japan, to an extent that you might not expect from reading the original article here.

Some of this is because societies are used to seeing very young women married off to older men, and some of it is due to the ongoing scandals and fear regarding younger boys being exploited by older men and women. The reality is that in some parts of the United States it's legal and accepted for a 14 year old girl to marry a much older man, but if you swap the genders many people would suddenly be upset - and the same holds here. There was an incident a few years ago where a magazine in Japan publishing relatively uncontroversial shotacon comics shut down permanently, reportedly due to government threats to enforce obscenity laws against it.

Now that we've gone down the rabbit hole a bit, it might be easier to understand why the mess with pixiv and the 'safe speech' vs 'free speech' types was so complicated.

On the one hand you have the 'free speech' advocates who really just want to be able to say what they want and post what they want. Some of them want to post death threats, harassment, or lolicon content - but let's be honest, it's not THAT many of them. For some of them it is also not targeted at any one individual, so harm is harder to argue even if it's content (like death threats) that would normally be considered harmful and even get you a visit from the police.

On the other hand you have the 'safe speech' group the article talks about, generally classifying them as people who are overly sensitive and want to police speech. This is true for at least a subset of that audience. Some people in that audience have come away from years of internet harassment and just decided they want a space where those people don't show up, so if it means hanging out with people who are really upset about anorexia, not much of a price to pay.

The problem is that lolicon and shotacon content conveniently blur the lines between these groups due to the intense legal threat they pose and the cultural controversy they present. At least for a western viewer, the moral and ethical implications of this stuff are VERY complicated and they might turn your stomach. That alone would make a server operator wary of letting this stuff get federated onto their servers - but the reality that it could get you tossed in jail is very real and it would make any sensible small business owner or individual run for the hills. Are the feds really going to care about the distinction between federation, caching or distributed cloud services when they show up to your door with a photo of some Clearly Not Appropriate lolicon content appearing in a social media timeline on YOUR website? Probably not. I hope you have a good lawyer.

The end result is that many server operators will end up fleeing directly into the "safe speech" territory, even if their personal preferences lie towards "free speech". This will naturally make the free speech group feel very oppressed or threatened when in reality the people making things hard for them are lawmakers and law enforcement. Naturally, in these sorts of disputes people tend to swipe at the target in front of them so you end up with trans women and proud boys shouting at each other on the internet.