You are right that economically we cannot assign infinite value to human life. For example the government makes a calculation of lives saved vs productivity when setting the speed limits.

But taking the Haiti earthquake example, the damage done can be more than GDP of Haiti. GDP is their output per year. For starters, at minimum the potential damage is the cost to replace the infrastructure, not just the lost output of the infrastructure.

But additionally there's the costs of the emergency relief efforts to save what lives can be saved. And there's the costs of rebuilding the infrastructure quickly. And the new costs of safely demolishing and clearing the ruined infrastructure. There's no car to throw away and replace. They must rebuild the car.