> If you force everything to always be passed by value and returned by value (never by reference) it's clear that the costs of constantly cloning all these objects would quickly add up.

That’s not what happens. See: http://erlang.org/pipermail/erlang-questions/2013-March/0727...

“Pass by value does NOT imply copying and never has; copying is only required for mutable data structures, and Erlang hasn't any.”