Foolhardiness, n.
Courage without sense or judgment; foolish rashness; recklessness. Dryden.
Shades of meaning
Fernald has no entry of its own for foolhardiness; he lists it under temerity.
Where he writes about it:
Venturesomeness dallies on the edge of danger and experiments with it; foolhardiness rushes in for want of sense, heedlessness for want of attention, rashness for want of reflection, recklessness from disregard of consequences. — from temerity