The thing that disturbs people the most is that Mt.Ebott is (according to historical records) the place where "Monsters" have been sealed long time ago. So if the missing people are underneath the mountain, they might get caught by monsters. Who knows what these monsters look and act like nowadays and what they might do.

You however managed to make it down the hole safely. You’re exploring the ruins of where Toriel used to live in. Before she went nuts and ate her own son. She still roams in search of human flesh but she’s hardly anywhere to be found.