As explained in the Editorial of Issue 13 of Plus , Arrow's Impossibility Theorem says that, in a certain sense, it is impossible to produce a consistent group preference by aggregating individual preferences. If this happens, then the invisible hand cannot be said to have worked to maximise economic wellbeing. In a centralised society a few individuals make decisions on how to spend everyone's money and direct everyone's effort. How economic systems work and what can be done to improve them is still very much a live area of research for economists. Political will, whether the world becomes more peaceful or less, and the practicality of any alternatives will also be factors.
Alternative systems tend to require much more intervention and more stringent rules.
In the real world, such rules automatically introduce more and more opportunities for mistakes and corruption, which might mean that another system, even if better in principle, would be worse in practice. Perhaps the strongest reason for leaving the allocation of effort and reward to the invisible hand is that when it misappropriates goods, it is likely to be on a small scale. More centralised methods of allocating goods are more prone to corruption and waste. It is useful to remember the context in which Smith developed his theories - that of a heavily planned and rather dictatorial society, where some individuals were above the law and others were effectively without any rights. In a centralised society a few individuals make decisions on how to spend everyone's money and direct everyone's effort.