Having a modular desktop environment kind of loses its purpose if a module (theme, extension) can bring the entire user session down.
Just this week, me upgrading a GNOME extension resulted in the user session completely crashing, getting me back to the login screen, and making me lose about half an hour of work.
Now, of course, I could put the blame on the sole developer that developed that specific extension (one of the preinstalled ones in Ubuntu now), but I don't. I blame GNOME that a botched extension update lead to the entire session crashing, instead of doing something normal (like reverting to the previous version and showing "update failed").
Just this week, me upgrading a GNOME extension resulted in the user session completely crashing, getting me back to the login screen, and making me lose about half an hour of work.
Now, of course, I could put the blame on the sole developer that developed that specific extension (one of the preinstalled ones in Ubuntu now), but I don't. I blame GNOME that a botched extension update lead to the entire session crashing, instead of doing something normal (like reverting to the previous version and showing "update failed").