If what you say were true, then we wouldn't be suffering from unemployment. We'd suffer from massive writedowns in our wealth (as we realize our malinvestments) but labor would be redeployed to new ventures. Effectively, we'd be working our assess off harder than before, but receiving a lower quality of life in return.
In reality, however, the economy is not at full employment. If we malinvested before (effectively did useless work), that should be a sunk cost. We wouldn't receive the future benefits we expected from that work, but that wouldn't preclude us from continuing to work. Malinvestment is not a reason for unemployment.
No, we're in a liquidity trap. Option A is monetary policy. That has been tried and exhausted. Option B is fiscal policy. Bring out the helicopters!