[makomk]

It consists of multiple daemons which are relied on by userland applications, are so strongly interdependent that the systemd developers don't support running them independently, and which have no stable or documented APIs between the different components. Oh, and many of them are infeasable to re-implement according to said developers.

Now, the Gnome developers may argue that technically Gnome doesn't require logind, and technically they're right. You lose the ability to shutdown, restart, sleep or hibernate your PC from the Gnome user interface - all things that worked before and that normal users expect to be able to do - but you can technically run without it. The API for those things isn't itself terribly complicated, but because the systemd and Gnome developers don't give a fuck about anything other than systemd they've bundled it together with a whole bunch of complicated, poorly-documented multiseat stuff that can only be implemented as one single, monolithic all-or-nothing API.

Which is, I think, part of the reason why Ubuntu gave up and is switching to systemd; they can hardly ship something that requires users to use the command line to shutdown or suspend their PC.

Edit: Also, the bit about how "we specifically approved some patches to allow Canonical to run logind without systemd" is... well, outdated is probably the politest way to put it. Since then the systemd developers have announced that they're breaking the ability to run logind seperately in future, they never supported it in the first place, and Ubuntu should never have done it.