<Vassili>I see the "classic" policy of disallowing the latter as an
arbitrary restriction, even when supported by emphatic
hand-waving.</Vassili>

I concur.  The restriction on assignment to arguments simply creates an
unnecessary semantic distinction between arguments and other variables, and
so adds complexity to the denotational semantics of Smalltalk syntax.  It's
not as bad as Java's distinction between objects and primitive values, but
it's a language design flaw of the same sort.

Bindings/assignments are not axioms, and Smalltalk is not a logic/functional
programming language.  Immutable bindings belong in a language where all
bindings are immutable.

--Alan