My point is that this isn't "reckless" - it's a core part of the value of a closure. We do this regularly enough in Ruby - usually with lambda rather than proc

My point is that this isn't "reckless" - it's a core part of the value of a closure. We do this regularly enough in Ruby - usually with lambda rather than proc/blocks because of the return semantics, but you can do it just as safely with proc/blocks as long as you don't call "return" within them (there's no reason to, on the other hand). It's a way of e.g. building generator methods that returns distinct callable objects without constructing a whole class. In that case the closure environment effectively becomes the instance variables.