Only the most optimistic Marxist can still believe that an entirely
controlled economy can work efficiently. Lack of inflation and full employment can
be mandated, but a flow of high-quality goods to the public
has never been generated by a Communist economy which can match
any ordinary Capitalist one. The reasons are not obscure.
1) Nobody knows enough. Large modern economies are too complex
for governments to be able to assemble all the information to
do rational and effective planning. Stock markets and corporate
elites may make irrational and even disastrous decisions, but
ultimately their mistakes tend to be self-correcting. These difficulties
are exacerbated by the fact that in a planned economy it is not
in the interest of most individuals to generate and convey accurate
data. The worker lies about how much work has been done, the manager
about how many goods are being shipped, and the economist about
how successful the latest plan has been. The official statistics
quickly become a fiction from which it is impossible to generate
any rational plan.
2) People are not motivated to work as hard for the common good
in large enterprizes as they are for themselves. This may or may
not be "human nature;" but no Communist government has
ever been able to inspire its people to work really efficiently
except for brief periods, usually through terror. Both the USSR
and China had to rescue their disastrous agricultural policies
by allowing farmers to develop private plots for their own profit,
which typically produced far more than the properly socialist
communal farms. Exceptions may be found on small Israeli kibbutzes
and other settings where people know each other well, but in large
modern states it seems impossible to generate the enthusiasm to
work hard except in wartime or similar crises. Toward the end,
the Soviet economy was notoriously rife with absenteeism, employee
theft, and idleness, expressed in the popular joke "they
pretend to pay us and we pretend to work."
Socialists commonly try to inspire workers with various slogans
and visions of the glorious future (say, during the Cuban sugar
harvest in the 60s), and these can actually work for a time; but
they seem impossible to sustain in the long run. After all, people
do not embrace socialism because they want to work harder: they
have capitalists to make them do that.