"But the sacrifice is too great" is a relevant argument, you think that "Yeah doing Y is right" is potentially mistaken.

I think I disagree with this. On a social and political level, the tendency to rationalize is so pervasive it would sound completely absurd to say "I agree that it would be morally correct to implement your policy but I advocate not doing it, because it will only help future generations, screw those guys." In practice, when people attempt to motivate each other in the political sphere to do something, it is always accompanied by the claim that doing that thing is morally right. But it is in principle possible to try to get people not to do something by arguing "hey this is really bad for us!" without arguing against it's moral rightness. This thought experiment is a case where this exact "lets grab the banana" position is supposed to be tempting.