I imagine some of those people fear that they did not discern “the signs of the times” properly, which means that God didn’t enlighten them, which means they might not be “saved.”
The whole dispensationalist system is unfortunate. It tends to reduce the Bible to a book of secret codes one must decipher.
The scary thing to me is these people put their entire existence into this idea. When you do that and suddenly it turns out to have been false, you get a very scary situation where that person can suddenly lose all mental stability.
To these people, this rapture idea IS Christianity and it IS God, so if the rapture is not real, then to them it must mean God also is not real, and that can cause these types to then see existence as pointless hence they no longer have any control over any violent impulses.