Ethan Zuckerman, Director of MIT's Center for Civic Media, recently blogged about the growth of Mastodon in Japan. Although started by a German software engineer, it's Japan where Mastodon has experienced the greatest growth. At the time of writing, three of the five most popular Mastodon servers are in Japan, with the top two (Pawoo and Mstdn) connecting more users than the next 8 servers combined.
Let's focus on Pawoo, the world's most popular Mastodon instance. Pawoo is a service of Pixiv, which is a sort-of Japanese version of Deviantart with 20m users. However, a visual topic frequently shared on Pixiv is Lolicon. The term, a portmanteau of "Lolita Complex", is defined on Wikipedia as
... an attraction to young or prepubescent girls, an individual with such an attraction, or lolicon manga or lolicon anime, a genre of manga and anime wherein childlike female characters are often depicted in an "erotic-cute" manner (also known as ero kawaii), in an art style reminiscent of the shōjo manga (girls' comics) style.
Both Zuckerman and Matthew Scala, in a similar post, attempt to strongly clarify that Lolicon is a sociably acceptable form of graphic culture in Japan, and in Japanese culture it is manifestly different to child pornography. In other words, in Japan, Lolicon = fine, actual child porn = really not fine. And because this distinction is difficult to comprehend outside of Japanese culture, it is hard for Lolicon "fans" (if that's the right word) to share images on a Western site. (Incidentally, we are not defending Lolicon at all. Far from it - this is a news article which aims to represent these events as a statement of fact.)
So, if you're a Japanese Mastodon user on Pawoo, then you'll have Lolicon at your fingertips. However, because Mastodon is federated, servers cross-fertilise their content with each other, and when Japanese Lolicon permeates into Western Mastodon servers, there's a crunch of understanding. Mastodon.xyz, a popular French node, has blocked Pawoo and other Western servers have done the same.
Now, if Lolicon is being freely shared by Japanese users who consider it to be a legitimate part of their culture, imagine the effect for other topics. Motherboard's recent enthusiastic commentary that Mastodon is like a Nazi-free Twitter and why aren't we all using it is, at best, naïve. As Twitter is unfederated and is served centrally, we can mute all of the Nazi shit if we want to (and, indeed, are able to). Mastodon's P2P architecture allows Nazi material - or, indeed, any other material one might find unappetising - to be freely distributed to servers which accept it.
Mastodon's increase in users will lead to someone at the Daily Mail using it eventually, resulting in a tirade about the "evil of Mastodon". This is a very important time for the social network; if it can resolve what is and isn't acceptable across each culture while intrinsically keeping its federated, private nature, then it could avoid being weighed down with the negative reporting that has dogged Twitter in recent years. Equally, however, Mastodon's federated nature will cause a great panic at the Home Office, where minister Amber Rudd has talked about UK users being prevented from using encrypted services.