The idea that multiplying suffering by the number of sufferers yields a correct and valid total-suffering value is not fundamental truth, it is just a naive extrapolation of our intuitions that should help guide our decisions.

I would say, instead, that it gives a valid total-suffering value but that said value is not necessarily what is important. It is not how I extrapolate my intuitive aversion to suffering, for example.

Sorry for all the emphasis, but I am sick and tired of supposed rationalists using math to reach the reprehensible conclusion and then claiming it must be right because math. It's the epitome of Spock "rationality".

I would say the same but substitute 'torture' for 'reprehensible'. Using math in that way is essentially begging the question - the important decision is in which math to choose as a guess at our utility function after all. But at the same time I don't consider choosing torture to be reprehensible. Because the fact that there are 3^<lotsofem>^3 dust specks really does matter.