It doesn't matter what Wayne has always said. He's designed a collection of fragile shell script hacks that want to be run as root that fundamentally change the behavior of key system commands.
You don't have to run them as root. You can run them as a regular user. I'm pretty sure Wayne recommends against RVM system-wide and the preferred method is just installing it for individual users.
login as regular user, download some version of ruby, compile for use as logged in user, install rvm, shazzam install any version of ruby you want - all of this only applies to the logged in user and has zero impact on the rest of the system. RVM rules :)
I no longer install ruby at a system level, not needed, only users running ruby stuff need ruby installed and never use distro ruby, creates all sorts of issues...