Why so?
The thing is all about Rob going back to get Beth. Its stupid and irrational, but the motive itself is beautiful.
Why does Lizzy and Hud encourage him and supported him then? They don't have to be stupid, rite?
Not to me, the two lost their love ones in the process, and because of that they would surely appreciate the precious times they spend together with their love ones, even it means death in the process.

Cloverfield is not about the logical emergence of a monster and the what's the world's most powerful and smartest people's solution for it, but rather focuses on the theme of the illogical things humans do when they go through a real nightmare, all by themselves, when they realize that what's most precious as life itself is so fragile; which is to me, what that makes us human.