I realise that’s kind of intrinsic to how mastodon works, but asking people to select an instance out of a whole load of them somehow feels like I’m signing up to be part of a cohesive group, which is unappealing to me.
I don’t use any social media because I think they’re unhealthy, but a few people I’ve spoken to have had the same stumbling block with having to pick an instance.
Trust the admin? Trust them how? Why? Doesn’t all of Mastodon abide by the same rules?
While you don't understand these issues, you can either rely on somebody else's advice for that, or join a server at random and see what happens. Unless you've joined the new Gab, you should be okay – if anything goes wrong you can just migrate to another server.
As for the things you've mentioned: you shouldn't assume your communication is private anywhere on Mastodon (there's some encryption proposals, but that's a long road from now), and you definitely should use different passwords for different websites.
All of Mastodon, or more accurately, the Fediverse, runs on the same communications protocol. By analogy, think of the World Wide Web (HTML), email (SMTP), or the cell-phone network (IMSI, amongst others).
A difference for the Fediverse from the World Wide Web is that Websites largely don't communicate with each other, but rather respond to specific requests from a Web client (e.g., a web browser), in a client-server model. The Fediverse, like email or the cellphone network, consists largely of peer-to-peer (p2p) communications between individuals, mediated by servers.
Specific instances vary tremendously in standards. My home instance (toot.cat) has a specific code of conduct:
<https://mew.toot.cat/mw/Toot.cat/CoC>
There are instances with highly incompatible rules and standards. Many of these are moderated (varying degrees of limiting interactivity, listed here:
Instance administration which is sufficiently unacceptable can result in near-total defederation of that instance, that is, few if any other instances follow it. Two notable cases involve a service operated by a former US political figure, and of a neo-nazi group (I'm not naming them, they're easy enough to find should you choose to do so).
Most mainstream Mastodon instances do follow reasonably compatible codes of conduct, though there can be regional differences. For example, some Japanese instances permit comic content (loli) which is categorically illegal in numerous other jurisdictions, and face limited interactivity on that basis. There are numerous other grounds for limiting interaction beyond that.
Again: this is similar to other p2p communications platforms in which abusive practices tend to give rise to limitations: Do Not Call registries, and under a phenomenal onslaught of robocalls, denying interconnects between telephony systems.
What group of people are you talking about and what sorts of rules do you expect them to follow?
Like we are rightly concerned about Google suspending accounts without recourse, but the rate at which they do that is still orders of magnitude lower than the personal fiefdoms known as Mastodon instances.
I have friends on Mastodon for some 5+ years and this isn't really an issue. If it actually keeps happening than either the instances you're picking are run by teenagers, or you're actually engaging in some sort of a behavior that perhaps warrants a ban?
Personally, am running my own instance so this is not a concern but the larger ones with good reputation tend to be mature about this. I'd recommend joining a well established instance but avoid the absolutely huge ones like mastodon.social
I don't think most people feel they "chose" their email at all.
How about something like: “Mastadon is decentralized, so instead of being one centralized service, it consists of many smaller communities. You can follow anyone in community, because they’re all interconnected. Moderation happens at the community level, by people who run each community. You can join any community that is accepting new members. This is more complicated because you have to pick where you want to join, but then you don’t have to deal with Elon Musk or whoever if you don’t want to.”
I haven’t joined Mastodon, but this is my understanding. Seems not that much more complicated if you’re already interested in not being locked into dealing with centralization. If you’re just looking for an alternative centralized network, then yeah this is probably confusing.
> provided it's open for new users
This in itself is a massive point of confusion for most users. I've had all my friends and family ask me about this very point and I didn't know what to say. Especially when Elon fired everyone, literally none of the instances on the Mastodon page were accepting anyone. It's much better now but this alone confuses people into thinking they're locked into their instance. Why would my father, a retired mechanical engineer, join an infosec instance? Or my friends join a French instance when none of us are remotely French?