If you're running off a cliff and you know there's a safety net to protect you, it makes the act of running off a cliff safer. Ergo, more people will run off the cliff.

What happens when that safety net vanishes as hoards of people are running off the cliff?

Edited to add:

This isn't really a theoretical issue, either. Risk is part of the price of a security. Something that has a high risk, may be valued less by investors. Often other investments will carry the same amount of reward but less risk.