To try and respond briefly, don't forget organizations that are using
Debian. For a lot of organizations, it's neither practical nor safe to
do a nightly upgrade on your hundreds of computers.
Also, don't forget that a lot of the reason "stable" is stable, is
because it sits frozen for a while and thus problematic interactions
*between* packages can be found and eliminated. If everything is
changing all of the time, you can't do this nearly as well.
I like releases! And I really like having separate "stable" and
"unstable" lines being developed in parallel!