Excellent summary. Yes, I did indeed conflate these two meanings of "pure" because I didn't want to get my post side-tracked into a discussion of this point.

Unfortunately if you want a language with industrial strength tools and libraries that is pure in the effect-less sense, Haskell is the only choice. So when I try to talk about the issue of effect management it sounds like I'm merely plugging my favourite language instead of making an argument about the importance of a fundamental property.