Also, me using Plex to host copies of my own software legally is not the same as operating a P2P service.

I'm not explaining this to you again. What you described is not legal on a US hosted service like Plex, and even most other countries with DRM exceptions for personal use do not include sharing outside your immediate household. Even if it's perfectly legal in your country, and the US can't touch you where you are, Plex is still obligated to abide by US restrictions. Good enough if that doesn't bother you, but it isn't completely without risk and you should be well aware of it.

if your concern is the govenrment overreach implications of having a portion of your data leaked, worrying about a smaller leak along the way of actively generating a larger leak is entirely pointless.

What exactly does "government overreach" mean in this context?

Using Google SSO independently is bad. Plex independently is bad. Using both together is worse. Using either while also breaking the law, when there's a perfectly acceptable way to do neither of those things and still just as easily break the law is a whole lot better.

Conversely, I’d argue that if you have a dozen users and are terrified that the cops are going to come and raid the… I’m gonna say meth lab you’re running on the side, we’re back to the conversation about how cool you are with that dozen users having their Jellyfin clients running on a bunch of Android devices, Smart TVs, Windows boxes or whatever else.

I'm just not a dumbass. Having a dozen users log in without any of them publicly pointing at me or my server IP is a hell of a lot safer than letting a private service log every sign-in and stream event of the server, and then letting a separate private service link those users to accounts with detailed personal information. Those people can install jellyfin on their phones and tablets all they want - google wouldn't know what servers those clients are connecting to anyway. And even if they did, my server is not associated with my personal details or ISP-assigned IP address. Maybe you just didn't know that, idk.

I came into this argument from the UX angle, you guys are increasingly convincing me that a significant disincentive for self-hosting to become mainstream

Using a google SSO isn't a prerequisite for self-hosting becoming mainstream. Maybe SSO generally is, but there are a dozen other ways to achieve the same thing. Maybe I don't care if it becomes mainstream? Maybe what I actually want is for people to learn tech self-sufficiency so that we're not indefinitely reliant on SAAS. Maybe i'm content with my special little hobby and I'd rather point and laugh at people who get fucked over by services they delude themselves into believing won't ever screw them, just because they can't be bothered to learn a new skill.

you guys are increasingly convincing me that a significant disincentive for self-hosting to become mainstream is that its entire community is convinced that they are doing something wrong, apparently

If you're as concerned with self-hosting becoming as mainstream as you claim you are, then I'd imagine you'd be more concerned with the late-stage capitalist reality of media distribution and the increasingly restrictive laws surrounding its use. Where I live, the legal structure that protects the right to self sufficiency is very much under question, and continues to get worse. I got burned several times in the napster/limewire days, before it was established precedent that sharing digital copyright material was illegal, and unheard of still that anyone actually got punished for it. I know better than most that you can't count on those protections indefinitely.

But as an anarchist, I think a little bit of crime is good, actually. More people should be doing crime. But if you're gonna do it, do the rest of us a favor and don't be a dumbass about it.