Yeah, Von Mises explicitly punts on that:
"The knowledge of the fact that rational economic activity is
impossible in a socialist commonwealth cannot, of course, be used
as an argument either for or against socialism. Whoever is
prepared himself to enter upon socialism on ethical grounds on the
supposition that the provision of goods of a lower order for human
beings under a system of common ownership of the means of
production is diminished, or whoever is guided by ascetic ideals
in his desire for socialism, will not allow himself to be
influenced in his endeavors by what we have said."
<http://www.mises.org/econcalc/CONCLUSN.asp>
Incidentally, Michael Albert has an interesting counterpoint:
"In a Participatory Economy we want to be Efficient.
"Does the word induce a bit of nausea in some of you? It does in
me. But we need to get over that, because efficiency really means
seeking to attain our aims and in doing so not wasting things we
value. We should all therefore favor efficiency. The alternative
to favoring efficiency is to favor either not attaining our aims,
or to favor wasting things that we value.
"So why does the word induce some nausea? In capitalism owners
preference become the sought after ends, and what owners value is
not wasted. So in capitalism efficiency means seeking maximum
profits while reproducing the conditions of profit-making without
wasting assets that owners can exploit. Capitalists don't mind
destroying humans with black lung disease, or exterminating humans
with weapons or with hunger, when the people afflicted are
expendable as far as profit is concerned. Capitalists don't mind
sickening people in the wake of their workplaces' pollution. They
don't mind blowing up or destroying assets that they themselves
can't exploit, though others will suffer from the loss. Under
capitalism being efficient means being vile, because it is a vile
system – and this is why we have some antipathy to the word
efficiency as it is used all around us."
<http://www.zmag.org/Parecon/writings/albert_lac.htm>
Tayssir