Why does God harden?

This question was asked to me recently. It's a common source of puzzlement because most of the Christian world today prefers not to speak about God's active judicial work of hardening.

"What need is there for God to harden/blind/make deaf unregenerate people so that they don't believe? According to our spiritual deadness apart from regeneration it is not possible for us to believe anyway..."

Hardening makes men more stubborn in manifesting their sinfulness, despite self-harmful consequences, despite their better judgment, despite external restraints.

Pharaoh is an excellent example. What kind of lunatic, even an unbelieving unregenerate lunatic, would refuse to let these people go when all these relentless plagues are completely destroying their country? It's a far greater blind insanity that is required. That takes a special kind of stupid. Then an even more special kind of stupid to try to double-cross the Hebrews by chasing after them, despite a pillar of fire, and even being so bold as to chase them into a passage surrounded by walls of water opened up in the Red Sea quite obviously for their benefit.

This kind of furious and tenacious rebellion against God requires a certain steely resolve, and iron courage in the face of such opposition that would be beyond belief, if not that we are told that it is God who supplied him with the strength to pursue his goal, while darkening his mind to the insanity of it.