One good reason for not caring about types: prototype code. I do a lot of prototyping (trying ideas quickly, not for production). I typically do that in python. In that case, I don't think types would be helping me at all, I can get run-time errors, but I don't really mind, it's an easy fix. I used to have to prototype in C++, definitely not the type of language that's fit for that (if only because it's compiled). Prototyping is best done with an interpreted, untyped language in my humble opinion...