It might be that people respond "Quite sensible" because your readers are trying to be rational, and conclude that both this and the "repugnant conclusion" are sensible conclusions.
Your restatement of the problem exploits my normative bias. It exactly mirrors moral parables we are trained on as children regarding intertemporal substitution and the nature of happiness. However, I am just as suspicious of applying such rules of thumb to population-scale moral problems as I am of the moral sentiments that object to the large world in Parfit's formulation. Moral intuitions that helped us thrive in hunter-gatherer and proto-agricultural tribes are simply not designed for problems of large-scale social organization.