If Sans wants to complain about humanity then he'll have an experienced and willing ear ready to listen... and maybe even to empathize, on a good day, but actually expressing that empathy effectively is an entirely different struggle.

"Seems to be a universal truth. Humans are also skilled when it comes to mistreating other humans." What a goddamn understatement. Still...

"I'll be clear and say I'm not accepting any fraction of the blame for what humans did in your dimension but I'll accept any of your biases against our species as something that can't be helped. 'Earth' and the 'Underground' are unfamiliar to me, but that's to be expected too."