Roughly speaking, a central authority might work in certain scenarios, for a short time, to prevent situations where market participants might otherwise panic.
In the long run, the problem is the same authority does not have to all "local", decision-making information available to the individual market participants, and that might prevent the economy from reaching an optimal configuration.
Everyone should know that free markets can allocate resources better than any central planner
and what the fed is doing is reacting to trends to prevent the system from tilting out of control, not centrally planning things (when the fed starts making 5-year plans then we can talk)
Old people want to keep their pensions and savings with 0% inflation or even deflation. The one thing they don't want to do is spend money, for obvious reasons. They'd burn through their pension very quickly.
An economy that is not spending money will die. Someone has to spend to keep it going. Interest rates must go to 0% or lower so that someone finally spends their money.