As was pointed out last time, if you insist that no quantity of dust-specks-in-individual-eyes is comparable to one instance of torture, then what is your boundary case? What about 'half-torture', 'quarter-torture', 'millionth-torture'? Once you posit a qualitative distinction between the badness of different classes of experience, such that no quantity of experiences in one class can possibly be worse than a single experience in the other class, then you have posited the existence of a sharp dividing line on what appears to be a continuum of possible individual experiences.

But if we adopt the converse position, and assume that all experiences are commensurable and additive aggregation of utility makes sense without exception - then we are saying that there is an exact quantity which measures precisely how much worse an instance of torture is than an instance of eye irritation. This is obscured by the original example, in which an inconceivably large number is employed to make the point that if you accept additive aggregation of utilities as a universal principle, then there must come a point when the specks are worse than the torture. But there must be a boundary case here as well: some number N such that, if there are more than N specks-in-eyes, it's worse than the torture, but if there are N or less, the torture wins out.

Can any advocates of additive aggregation of utility defend a particular value for N? Because if not, you're in the same boat with the incommensurabilists, unable to justify their magic dividing line.