It requires the use of force to redistribute weatlh. It also removes the price mechanism, thus robbing the people of information required to produce and evaluate.
What if we just gave everyone like vouchers or something that they could use to trade for whatever they wanted? Although, how do we encourage people to do work that's more important than other work? Or people who have skills that are in short supply? And how do we make sure that people don't hog the stuff that takes a lot more work to produce? Maybe if we gave people more vouchers if they worked in more difficult or more needed jobs, and maybe we could make it so that the stuff that takes more work to produce requires more vouchers to trade for. But then how do we set the values for such things? Who could possibly collect enough information to get all the ratios right? Oh wait, who knows better than the people who use goods and services? What if we just let them set their own rates for voucher exchanges and let everyone sort out things on their own? That way people who have skills that are rarer or more needed by the public will be able to collect more vouchers and people can choose what goods and services are most important to them personally by deciding how many of their vouchers they're willing to give up for them.
There you go, I think I fixed communism.