Programming concepts come more easily the more gradually they are revealed. Nobody has any concept of what a stack overflow is or why it's important on day 1. Ruby is approachable and fairly forgiving and (at least in MY opinion) VERY readable.

Full disclosure: I went to engineering school for 2 degree and then later attended (and currently work for) a code school.

I can say that I can see a marked difference in students that go through Ruby as a first programming language vs JS. Ruby-first students are more ready to deal with new ways of doing things and they are, in general, less likely to have serious learning issues. JS-first students tend to have more consistent problems grasping things like scope and return values. It IS possible it's bent as such due to our curriculum, but all I can tell you is what I've seen in our students.