I have no opinion on its ability to replace Twitter, but the federated nature of Mastodon means that an instance can disconnect from the instances that are hosting spam accounts, much the same as many instances have disconnected from servers that host racist and alt-right communities and accounts.

It seems to me like you don't understand the crucial difference between Twitter and Mastodon.

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.

Regardless of the technical measures, I think we can all agree something called 'Mastodon' will be safe from spam bots in perpetuity simply by virtue of not having any non-geek users.

"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..."

Why do we need to identify and ban those in the first place?. When I used Twitter I never thought "oh man, these spam bots are ruining my twitter experience". It was more like "Oh, another bot is following me". Didn't waste more than 2 seconds of my day.

Yes, of course. However, if I'm not mistaken, each Mastodon server instance creates their own policies regarding what other servers can tweet to their users. So it would be trivial for any Mastodon server to "ban" Twitter users from posting in their instance.

You say that like Twitter declaring bankruptcy would be a bad thing