I agree, you have to just multiply.
But your math is an attempt to abstract human harm to numbers, and the problem I have (and I suspect others intuitively have) is that the abstraction is wrong. You’ve failed to understand the lessons of the science of happiness: we forget small painful things quickly. The cost of a speck in the eye, let us imagine, is 1 unit of harm. But that’s only true in the moment the speck hits the eye. In the hour the speck hits the eye, because of the human ability to ignore or forget small pains, the extended cost is 0. This is why a googol of specks is better than torture, because a googol 0s...
The real problem is defining the boundary between momentary (transient) harm and extendable harm. This is a psychological math problem.
I agree with Thom Blake: “Everyone has a right to their own opinion” is a defense against unreliable hardware. Your opinion is wrong so I must kill you and take your women, or even just your opinion is wrong so I must repress you.