The truth is, startups are much less secure, have in many cases serious problems in terms of future opportunities. And most importantly - despite saying "the job market is great, you can always find another job", this is just historically false.
Please, read what Patrick Mckenzie has to say on the matter here: https://news.ycombinator.com/item?id=7611848
And Thomas Ptacek's writing on this as well here: https://news.ycombinator.com/item?id=7612575
"When Sonicity failed in 2001, I had a track record as a lead developer on a successful, well-reviewed enterprise product, the lead engineering role at an ISP that might still have been among Chicago's most popular, and research publications at least one of which has a cite record that a lot of ACM journal submissions would envy. Not to mention, I had cofounded a company that had raised a significant amount of money. I was living in San Francisco at the time. I had to move to Ann Arbor to find my next job."