If you ask people to give you a clear alternative of a poltiical system then the only way to give you what you are asking is to give you something that migth work in theory but that's not based on empiric reality.

One of the big problem with Soviet style communism was that a central planner made a plan with wasn't well based on empiric reality.

As a result there are valid reasons for part of todays left to dislike the idea of central planning.