On gitter.im's red/red/welcome, Nenad Rakocevic said::
"Redbol languages are based on denotational semantics, where the meaning of every expression needs to have a representation in the language itself. Every expression needs to return a value. Without unset! there would be a hole in the language, several fundamental semantic rules would be collapsing, e.g.
reduce [1 print ""]=>[1](reducing 2 expressions would return 1 expression)."
I suppose he hasn't read Godel, Escher, Bach.
The fact of the matter is that there is no such thing as a "complete" system. All we do is push complexity around in order to shape the territory to become suitable for our purposes.
Somehow, the idea that reduce [1 print ""] could be an error is by its definition worse than having a block that holds a "unset value".
It's strange how uneducated minds work.