Its their fear of confrontation and anxiety manifested. They are so scared of everything that they'd rather kill themselves than deal with the very idea of the hardship happening. Ironically, when it inevitably does happen they don't have nearly the same breakdown, because humans are resilient like that.

Which they think applies to everyone. They are so self centered and full of protagonist syndrome, they can't even comprehend someone else isn't full of that same anxiety and terror. So they want to kill them to to spare that horrible fate they made up for them.