Sans doesn't have to imagine. We know what he thinks; he asks this any time his brother got killed by Frisk. Sans believes this kind of power must be used to make everyone's lives better. At the same time, Sans made Frisk promise NOT to use their power now that he and the other monsters got to the surface, even if Frisk suffers horribly under the pressure. In a sense, he's forced Frisk into the same situation that drove him into absolute despair: Knowing resets exist but being powerless to do any. Sans gave up, Frisk keeps going on.