I was going to respond to a few things, but you linked to ESR's guide, the most condescending guide to hacking I know. Anyone who links to this guide seriously is usually not going to be swayed by even the best arguments.
I think that starting with both Python and Ruby is
a bit strange idea - they are really similar (in almost
every way I can think of)
Exactly the point. They are so similar that the transition from one to the next is easier than most other languages. Once you have an easy transition students will notice similar patterns. "Oh, looping. Hey, this is something that happens in both languages."