The tough thing is that for the vast majority of end users, the interface that they see is the software or service. So if their instance has a bunch of disgusting pornography, as far as they’re concerned, mastodon has a bunch of disgusting pornography. For a lot of folks, the browser/server abstraction for regular websites and how that differs from native apps is about as far as they’re willing to go in their understanding of Internet architecture and for many, it’s too far. Requiring people understand that not all mastodon is mastodon despite it being kind of the same, in order to avoid explicit hentai, is a non-starter. My grandparents are dead, but they would probably take their computer out back and set it on fire if that shit flashed up on their screen. They sure wouldn’t have used it as an opportunity to get all of the base knowledge they needed to even realize they had to instance shop. Facebook is just riiiiight over there.