Are you suggesting that Mastodon has a better system for identifying harassment, spam, and spam accounts? Or that, given that they're mostly friendly early adopters, they haven't yet encountered the problem?
There's no such thing as Mastodon, a singular social network. Mastodon is a series of instances that talk to each other. A sysadmin running the instance can do whatever he pleases in his instance, including closing the registration, banning entire instances from communicating with his instance, and enforcing whichever rules he wants to enforce.
Mastodon doesn't deal with such issues at all. It's sysadmins running Mastodon instances that are supposed to deal with such issues.
It's more like reddit, where mods of subreddits have nearly complete authority over their own space on the social network, than it is like Twitter, in which a single entity is in charge.
Oh wait no we don't.
So, in your opinion, Mastodon nodes - by virtue of being federated - would be better equipped to handle the spam and harassment volume that Twitter is subject to?
I find that hard to believe.
ActivityPub (and OStatus, and ActivityStreams/Salmon, and OpenSocial) are all great specs and great ideas. Hosting and moderation cost real money (which spammers/scammers are wasting).
Know what's also great? Learning. For learning, we have the xAPI/TinCan spec and also schema.org/Action.
"Hey Melissa, here's my Mastodon handle, hit me up."
"Your... what?"
"My Mastodon, it's a federated social network free from any corporate overlord!"
"Whatever, freak..."
BTW Mastadon sounds like it's related to BDSM or ED meds IMHO.
"Sweetcheeks, have you heard of Mastadon?"
"I'm not into that dear!"
or
"When the moment is right... Ask your doctor about... Mastadon"