You'd need to change that to 10^6 specks and 10^15 frogs or something, because emotional reaction to choosing to kill the frogs is also part of the consequences of the decision, and this particular consequence might have moral value that outweighs one speck.

Your emotional reaction to a decision about human lives is irrelevant, the lives in question hold most of the moral worth, while with a decision to kill billions of cockroaches (to be safe from the question of moral worth of frogs), the lives of the cockroaches are irrelevant, while your emotional reaction holds most of moral worth.