Low interest rates and easy money has created debt. Massive bubbling amount of debt. Crashing debt bubbles is not fun, just ask anyone that lost their shirt in 1929. There is a paper[2] from this past June that goes deep into this, highlighting how and why debt bubbles are so dangerous. TL;DR? At least checkout this Bloomsberg article[3].
I think there will be a number of unicorns that are successful. I don't even think this will only be those that are profitable. Like always, there are companies that are overvalued, and some that are undervalued. I don't think it's a 10/90 split as has been suggested by some, but the next couple years will certainly be interesting.
[1] http://blog.samaltman.com/the-tech-bust-of-2015
[2] http://conference.nber.org/confer/2015/EASE15/Jorda_Schulari...
[3] http://www.bloombergview.com/articles/2015-06-26/the-reason-...