It's full of instances with definitely illegal, and possibly borderline-illegal content, and even worse - spam. You have to extensively, and aggressively blacklist, to avoid getting flooded in this crap. (And unless you want to wade knee-deep through that dreck, what you do, is to just copy & paste a blacklist some other poor bastard curated. I'm sure there's no vector for abuse, or censorship there...)
Mastodon also fails to solve the harassment problem. Facebook and Twitter do a piss-poor job of it, but Mastodon takes it to another level.
> The attack vector looks like this: a group of motivated harassers chooses a target somewhere in the fediverse. Every time that person posts, they immediately respond, maybe with something clever like “fuck you” or “log off.” So from the target’s point of view, every time they post something, even something innocuous like a painting or a photo of their dog, they immediately get a dozen comments saying “fuck you” or “go away” or “you’re not welcome here” or whatever. This makes it essentially impossible for them to use the social media platform.
> The second part of the attack is that, when the target posts something, harassers from across the fediverse click the “report” button and send a report to their local moderators as well as the moderator of the target’s instance. This overwhelms both the local moderators and (especially) the remote moderator. In mastodon.cloud’s case, it appears the moderator got 60 reports overnight, which was so much trouble that they decided to evict Wil Wheaton from the instance rather than deal with the deluge. [1]
The problem is that Mastodon conflates identity, and community. You will get moderated by third parties for belonging in a particular community, if that community is poorly moderated. Because the definition of poorly moderated is universal, you get a balkanized, political nightmare, where half the toots half the world sends are unreadable to the other half, even if the sender is not personally violating any rules of either community.
For a social network in 2019, this is unacceptable.
Oh, and if you're one of those people who cares about privacy, the only reason Cambridge Analytica, and its ilk aren't harvesting data from Mastodon, is because it's irrelevant. Yes, you can have private conversations with a particular group of users on it, without leaking data. Guess what? You can do that through e-mail, too. As soon as your toots are public, they can be scraped, your social graph can be re-constructed, packaged, and sold to the highest bidders.
[1] https://nolanlawson.com/2018/08/31/mastodon-and-the-challeng...
[2] https://www.theverge.com/2018/8/31/17801404/mastodon-harassm...