Learning a new language requires that you adapt your way of thinking. Idioms are a way to familiarize with the spirit of a language.
Starting to teach languages avoiding what makes the language so special is counter productive. As soon as your students know a basic way to program, they won't be inclined to learn the "good way".
I'm not sure how else to say this, but taking things out of context still does not make them wrong. This is about teaching the concept of programming. If you're learning a particular language, yes, use the idioms. If you're teaching someone how to code, teach concepts that cross languages.
Starting to teach languages avoiding what makes the language so special is counter productive. As soon as your students know a basic way to program, they won't be inclined to learn the "good way".