In my opinion, the difference between Mastodon/ActivityPub/the fediverse and email is adoption. If Mastodon was more popular:
- A handful of instances provided by large companies would probably crop up and end up hosting the majority of users
- Spammers would notice that they could reach a large number of people via Mastodon, and start spamming
- The providers of these large instances would moderate heavily to prevent their own instances being used for spam, and begin blocking / not federating with small instances
I should add that spam is probably _already_ a problem on Mastodon, but perhaps not to the extent that it is for email since the average Mastodon user is (for now!) way less likely to fall for a scam and therefore a much less valuable target.
The other problem with Mastodon / the Fediverse is how fractured it is. Here[0][1] are some examples of the sort of blocks that instance admins implement, including reasons such as "Allows controversial content" and "A lot of trolls, very [My Little Pony] themed".
I suppose it is to their credit that these instances are so transparent about their blocking policies, but I think the world would be a worse place if email or even Twitter made it impossible for people with different politics to message each other.
- A handful of instances provided by large companies would probably crop up and end up hosting the majority of users
- Spammers would notice that they could reach a large number of people via Mastodon, and start spamming
- The providers of these large instances would moderate heavily to prevent their own instances being used for spam, and begin blocking / not federating with small instances
I should add that spam is probably _already_ a problem on Mastodon, but perhaps not to the extent that it is for email since the average Mastodon user is (for now!) way less likely to fall for a scam and therefore a much less valuable target.