[anoctopus]

Immutability was what I had in mind calling it opinionated, and it's an opinion I agree with. After learning Clojure, I now hate working in languages with mutability. It obviously isn't necessary to make working applications, but I like not having to think about where else I'm passing this particular data structure, and the language has enough escape hatches for places when it really would get in the way.

[kazinator]

This is merely a psychological issue, because when you're programming in an "everything-mutable" Lisp dialect, you also don't worry about this. If you don't know where else you're passing that data structure and don't care to find out, then ... you don't mutate it. Libraries and API's simply don't mutate the inputs that you pass to them, unless loudly documented otherwise. Thus, mutation is applied in controlled ways whose scope is easy to ascertain and limit by inspection.

[qwertyuiop924]

...Especially in Scheme, where mutation is, by convention, loudly proclaimed! (not-quite-pun intended)