There are probably some generalizable differences between software engineers who work for intelligence agencies vs private sector engineers. The most significant factor being that government engineers need to be able to get a security clearance and pass the attendant background checks and interviews. Most of the engineers I've worked with in the private sector probably couldn't pass these checks because of foreign nationality or recreational drug use. It's a virtual certainty that the need for a security clearance produces a strong selection effect. Not saying it makes the intelligence engineers better or worse just that I'm sure there are some significant differences.

I just wanted to point out that obtaining a security clearance is not nearly as hard as you make it sound. For most organizations prior recreational drug use does not preclude you from the clearance.

I have a clearance and a somewhat checkered past.

A lot of what they look for is consistency in accounts of previous behaviors between you and any references / interviews they undertake, trying to assess if you're currently honest.

Another big thing they are trying to decide is if you are blackmailable.

(throwaway because I have the sort of clearance you are not supposed to advertise that you have)

John McAfee discussing getting his security clearance when he worked for Lockheed-Martin: "They asked me very revealing questions.... Had I ever taken drugs? Yes. What kinds? Almost every kind. Uh, how much? A lot. Have you ever sold drugs? Yes. So I assumed I would never get the clearance but I did and it came in very quickly."

(clearly decades ago, and he's less than reliable, but fun nonetheless!)

It's not so much a problem if you do drugs.

It's a problem if you do drugs and are hiding it from someone (say, family). Then you can be blackmailed.

Can confirm (source: I have a friend that works for a three-letter agency). Before I sit for a clearance interview, I asked him about it. I used to think I'd probably be disqualified, but I learned that was not the case at all. Much of what they're trying to determine is your exposure to potential blackmail.

How recent? Posts like "FBI can't find hackers" have been frontpaging for years but people who have responded to the ads say they were dismissed at the clearance step or advised to not continue due to it.

Sure, Facebook and Google are pretty evil organisations but they can never match the scope of surveillance of governmental agencies.

Facebook and Google need the user to use their services and they say (despite the message being in legalese) what they're going to track. There is consent involved in these organisations, it's a voluntary transaction.

The government can (and did) just intrude on everything without consent or penalties.

From a moral point of view, I would be open to work for BigTech, but I wouldn't work for a state actor.

In theory, yes. In practice, if you'll try to avoid any interaction with sites affiliated with Google, Facebook or feeding surveillance data to them, you'll quickly discover that the internet became very small and much less usable than before. You don't need to use Facebook or search on Google to be tracked by them. Google owns one of the largest ad networks in existence, so if you visit any site that has ads or analytics trackers, the data about it will go to Google. Any site featuring Facebook social button may feed the data to Facebook. If you write to somebody with @gmail address Google knows about it. And so on, and so forth. For a highly technically skilled person, it might be possible to avoid interactions with Big Tech while being able to still using modern technology, but it won't be easy. For a normal person without deep technical background it's pretty much hopeless unless they avoid using the internet entirely. Of course, using the internet is "voluntary", but this is a very weak consolation.

And, also, both Google and Facebook eagerly cooperate with state actors in censorship and other aspects - likely surveillance too. So there's not much difference in that aspect whether you work for the government directly or for somebody who takes marching orders from the government while being formally independent.