I am not going to say that the current packaging scheme is ideal, but to say that Ruby shouldn't be packaged at all on systems like Debian and Redhat is to ignore a lot of the very real good that has come of quality package managers like dpkg/apt and rpm.
One use case would be if someone, say a sysadmin, wants a good bug tracking system for internal use at their company.
apt-get install redmine
Fetches Rails, Ruby and so on, and sets it up in a default, reasonably secure way (as far as I know, I haven't the Debian version myself).
That sort of thing is pretty commonplace with PHP web applications under Debian and Ubuntu. Granted, if you're going to hack on and modify the application in question, yeah, you may want to get it and install it yourself, but when things work well, a good packaging system lets you install and work with code that perhaps you do not know intimately.
I think you're making the mistake of viewing the world exclusively from the point of view of a Ruby developer. What would happen if you had to deal with different systems to install, maintain and upgrade the Linux kernel, Apache, Postgres, Sqlite, Ruby, GCC, Perl, Python, Gnome, and various submodules used by them? There are times when it's necessary to install your own version of something, but it's awfully, awfully nice that you can "choose your battles", and really only do that with stuff you care about and follow closely.
Sounds like Linux in the days when you installed Slackware and then just upgraded stuff by randomly recompiling bits and pieces every now and then.
BTW, I would hope that we could skip any "angry disagreements" here. Passion will do more than suffice!