Macon Ravenwood refers to Mortals (like us!) as "beautiful creatures" (2.4.83). He says that he envies our (yeah, we're still including ourselves here) persistence and our undying belief that we can change things. He's right, though. Who hasn't wished they could change the past or the future? Who hasn't fought impossible odds to fix something even when everyone else thought it would never work? And you know, sometimes we even succeed.
Lena's uncle is a Lilum, a demon. He abides by a different set of rules than we do. He feels trapped by fate, like he's just floating down a river and can't do anything to alter its course. He says he envies us, sure. But his words almost sound like pity. It has kind of a condescending "silly humans, free will is for the birds" tone to it.
But he called us beautiful. And we like feeling pretty.
Macon is a foil (an opposing force) to Lena's Dark Caster mother, Sarafine, who refers to Mortals as "disgusting creatures" (2.11[3].64). Sarafine only sees the bad in humanity—the gluttony, the sloth, the hatred directed toward fellow man. In all honesty, she has some valid points. So why not go with her side for the title? Our answer: Disgusting Creatures just doesn't have the same ring to it.