For engineers above a certain skill level it's difficult to imagine job security becoming a real concern in the foreseeable future.
You're certainly correct about the opportunity cost of forgoing higher guaranteed comp at a BigCorp in return for a potentially higher reward, but I don't think that directly relates to the question of job security.
Do you remember 2001? One moment everything was brilliant. a year later and I had people who were working alongside me... people who were better than me in the late '90s... working for me, because their other option was retail. "I can't pay you what you are worth," I said to an ex-coworker I found working in a sandwich shop in the mid-aughts, "But I can pay you more than this place does." The guy really was pretty good, and he ended up working for me for many years.
Now, maybe we are in a bubble and maybe we are not, but the tech sector has a history of very sharp ups and downs, and in the downs? my experience is that a lot of pretty good people end up un[der]employed.
The other interesting thing is that from what I've seen? Layoffs at big companies (and if the sector takes a dump, there will be layoffs) are generally more "fair" than interviews at the same places. By that, I mean that those people who are shy but good are often the last to get laid off, but beyond a certain level, when interviewing, the "shy" part hurts you more than the "good" part helps you.
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.
The thing about the daisy cutter that Patrick said is not a myth. If you're one of the people here that believes we're in a bubble, you should take it seriously. They didn't call 2002 "Nuclear Winter" for nothing.
When my employer failed in 2002, I had no trouble getting another job offer. Unfortunately that company failed before my start date. As did the one after that.
I moved to NYC to get a semi-functional job market.
These days the possibility of highly correlated failure is a major component in my career decisions.
You're certainly correct about the opportunity cost of forgoing higher guaranteed comp at a BigCorp in return for a potentially higher reward, but I don't think that directly relates to the question of job security.