Because I have seen the horrors that they wreak in a production system where they are responsible for mission critical logic.

The horror. The horror.

Could you give examples of it ? You could also write horrible python or ruby code.

I don't feel comfortable posting code from my employer here, sorry. But let me address your counter-argument on its own: Saying you can write bad Ruby or Python is a turing tarpit argument. You can write bad code in any language, but I've seen a lot more bad shell script code than I've seen bad Python. Add to that that shell scripting languages are very irregular and I can't see why anyone would use a shell script for something that they actually relied on that was more complicated than invoking a few commands in sequence.