How about thinking the other way around:
Can you, or anyone else for that matter, explain to me why this is better than commercial interests not following us around at all?
> turn off third-party cookies, but a bunch of the internet breaks if you do that
Most of what breaks is just tracking for ad serving purposes. I'm fine with that breaking.
Some authentication services have trouble, but there are other ways of implementing that, so they could be fixed without needing to keep 3rd party cookies enabled.
> I expect that most sites will be forced to make themselves work without third-party cookies
As they should, if competently designed.
> … but naively I'd rather …
Call me dogmatic, but I'd rather not be followed around at all, even as a group. I don't trust that the data cannot be de-anonymised in any way, and I don't trust a company that would gain from that to do its best to make sure it can't happen.