The only substantive argument I can see is that the technology is immature:
> Well...without exposing our services to the public internet and forcing our friends to signup for our weird app
Which, yeah, of course the tech is, there's only like a dozen people doing this. The exact hurdle named is hardly insurmountable: in the standards, OIDC overcomes this¹, or guest links. I don't want my family signing up for my weird app either.
One of the other big hurdles is that ISPs like to sell "Internet access", but only deliver half the deal. If you're not getting IPv6 connectivity in the year 2025, I'm sorry, that's a crippled product that your ISP was defunct and didn't properly inform you of when they sold it. (It's a lot easier to self-host on the v6 Internet. Some of my personal services are v6 only b/c of that, and that it works well enough in all but the most extreme or temporary locations.)
(¹but the half-baked OIDC implementations out there might require you to pre-register your app with them. That, rightly, might be a PITA.)
It comes off to me as the author not wanting to do the hard stuff of working towards their values. Just kind of defeatist and trying to make a splash but leaning on a pretty weak premise.
Nominally, yes. In terms of that meaning anything, no. The benefit of ownership is not exclusivity, but control. If the library doesn't have a book (or other piece of media, of course), I have no power to influence them to get it despite that theoretical ownership. If the librarian decides a book is offensive and removes it from the collection, I have no power to influence them to keep it. I have to live with someone else's decisions about what the library does and does not contain, just like with a commercial service. So my nominal ownership really means nothing at all.