It's not about punishing the foolish, it's about maximizing the utilization of societies resources. If you hand ten million dollars to a fool and he squanders it, he's not the only one that loses.

The best reason for a meritocracy isn't fairness or justice, it's the benefits it creates for everyone. When someone smart is given control over resources, they create more resources, for themselves and others.

When that someone smart creates more resources, isn't is likely that they're in a better than average position to plan for its distribution, specifically including placing those resources under the control of smart people to utilize them?

I trust the creator of wealth (small, medium, or great) to allocate it intelligently far more than I trust a bureaucracy to do so.

Hence the need for a meritocracy.