There’s no retort. If anything, Jim’s rebuke is a bit magnanimous. His actions to him reflected the savagery that was hard wired into his DNA, a step above the rationality that Starfleet as a whole tried to keep at their core.

Alexander Marcus had made it seem like it was nothing more than timed disaster to explode over galaxies as opposed to one building.

At least, from Khan’s skewed perspective.

"No. I cannot." Says the man who is seeing less hope the more he learns of what it is they are facing and their slim odds of success.