I think this manga played to our most basic of narcissisms, and the fact that we all want somewhere to belong. The fact that it destroyed them was in the writers dark point of view.

For those of you wondering about the people reaction inside the tunnels. The tunnels were at an angle sloping down inside the mountain. So no matter how hard you struggled you had no choice but to move forward. Also the extremely tight fit, combined with your inability to control your movement would trigger your bodies survival instincts of intense fear and loss of all logic.

I still understand that the premise of this story makes little or no sense, but I'm trying to explain that the reactions once inside the tunnel are quite realistic. But there is no way you could ever get me inside one of those things, regardless of how much it looked like me.