I feel like this is a major oversight to how lemmy works. I feel like instances should be able to maintain overall federation, but 'disable' another instance by default, so that it's virtually invisible unless a user turns it on themselves. NSFW tag is way too broad, it encompasses so much more than porn
The concern is often not preventing their users from seeing the content but preventing their servers from "hosting" to the content for liability reasons.
If you're using an app, instances like pornlemmy.com wont work. They say it's because theyve made so many changes to the layout. I use Connect for Lemmy, and have been able to circumvent this by making an account on pornlemmy.com and logging in via my app, now I have all my needs satisfied. (Also kind of convenient as now it stays separated from my main feed)