99% of variables are local to your function, is not like program a thousand of global variables.

Sounds like you code pretty tight. I've seen plenty of functions reference variables out of function scope, or be reassigned within long function bodies. I personally don't code that way, but not everyone does. And as you've seen in this thread, there are people that do like immutability. To each his own.

I do prefer immutability too and think it should be the default for most programming, my original point was that for me, the trade-off of using clojure (small ecosystem) instead javascript for single server CRUD apps is not worth it but as a language I'll take clojure over javascript any day.