All systems are defenceless against actions at a level which is sufficiently meta. However most threats happen at a level where systems are given a reasonable chance to defend themselves. Here it becomes obvious that some systems are better than others at ensuring their own stability. Hence, instead of giving up on security (because there is always a level at which it is unsustainable), we should strive to create systems which not only provide a sane experience, but which also try to minimize the abuse of authority.

Smalltalk and Common Lisp may indeed be cool reflective environments, but it is undeniably the case that they do not provide adequate security if we wish to elevate them to operating system status. For further discussion, see SmalltalkSecurity. This problem is, at its most optimistic, a reason to improve the family tree. Newspeak is a great start. (Clojure not so much, but it has never claimed to be an acceptable Lisp Machine system language).

(Stanislav Datskovskiy should really consider fixing the comment section of his blog)