If you're going to write unreadable code why not use Perl? It's much faster than Ruby. Or Awk, even though it's one of the worst programming languages ever created?
Ruby (and Perl) can and probably should be used for many tasks where you might use awk and sed and don't particularly care about performance.
An argument "against readability" is culture. For sysadmins, Perl is a well-known language; it's not unreadable¹. Note that the same applies to Bash, and Bash scripts are still popular. This doesn't imply that Perl/Bash scripts should be universally used, but that within a certain culture, they make perfect sense.
¹=when talking about oneliners