That’s what I personally prefer in an instance (and it’s why I use lemmy.today as my home instance, which doesn’t defederate), but:

• You gotta remember that admins are running these instances mostly on their own dime. Like, some people aren’t comfortable donating to host content that they are upset about.

• Some content is…a major turn-off to a number of new users. Like, I think that if the first instance a random new user joins is, say, hexbear.net, it might turn some users off the Threadiverse. Maybe that should be provided with some sort of curated feeds that users can optionally subscribe to, and I understand that BlueSky does something like this, but as of now, the Threadiverse can’t do this.

• The Threadiverse spans a number of legal jurisdictions. Some have laws that one’s instance might run into. Admins may not want to get in trouble with the law.

• Ultimately, while it complicates things to have a variety of instances with different rules, it does make it more practical for people to find exactly what they want. Like, beehaw.org has fairly restrictive policies aimed at keeping a safe space for some users, and they defederated with lemmy.world way back to do that. That’s a very major defederation. That’s not really what I’m looking for in a home instance, but for people who do want it, it lets them find an instance with an environment that they want. If they don’t like that, well…there are lots of other instances out there with different policies.

  On Reddit, there was one admin team, one set of policies, and you didn’t have any choice. Your options were the rules that they chose, or you don’t get to use Reddit. On the Threadiverse, there are countless options, and if there are no instances that do what some people want, they can create their own instance run a new way.

EDIT: I would bet that maybe some people are thinking “well, people who object to pornography are prudes, and the Threadiverse needs to tell them to knock it off; they can just filter at the user level”. To give a concrete example showing why someone might want an actual defederation as opposed to just a user-level filter…I used Reddit back when the /r/jailbait thing became a major piece of drama in the US. So, this subreddit was devoted to showing legal (well, in the US, anyway; laws vary around the world) content showing young girls. Under the subreddit rules at the time, it shouldn’t deal in underage pornography, but it certainly skirted the edges. /r/jailbait had become staggeringly popular at the time, and had grown to become one of the top few subreddits on Reddit. When you searched for “reddit” on Google, Google would provide a set of links to the top few subreddits to help people find them, and so it’d show /r/jailbait prominently among the top four or so subreddits. While I don’t think that it was in the default list of subreddits that showed up for new users browsing the front page, the Google listing made it very visibly associated with Reddit, and I remember a lot of people saying that they were really uncomfortable with regularly visiting, at work, a site that maybe, say, their manager glances at and associates with images that are borderline legal. At the time, there were stories on national news about the fact that Reddit was running said content.

Okay, so you’ve got one camp that’s would like that content to be available. You’ve got another camp that doesn’t want to even use a site that has the subreddit available in any way, even if they personally don’t browse that subreddit, and certainly is unhappy about having the site prominently associated with this kind of content. With Reddit, the admin team has to make one global call on /r/jailbait. No matter what that call is, some people are going to be happy with whatever they decide, and some people are going to be upset. With the Threadiverse, you can go off and run an instance that has access to something like that, or you can run an instance that defederates with any instance that has local content like that.

As the fediverse grows, you can’t just assume that everyone connecting to it is an adult. NSFW content needs to be segregated by default.