> because they were doing their job

Where have we heard that one before?

Not to defend the op, since I think they're taking a particularly hard line, but qualifying candidates based on their previous work is just something that happens.

I've personally been disqualified because I've worked at a legal, but "vice" based company - I've seen others not hired because their previous company was too "legacy", even though they did very similar work.

It's not necessarily right, but companies use the signals available for them - even if they're not 100% agreeable to everyone.

I'd like to emphasize the nature of the answer which was a defensive "I was just following orders".

At that point, I was conducting dozens of interviews a year, and I think that sort of question came up... maybe three times? One of those people was from a medical company with a very large and very embarrassing contemporary incident, and the interviewee and I talked about development process problems. In fact, they admitted, it was part of the reason they left! We hired them and I enjoyed working with him.

exactly this... I think there are more factors at play than “Didn’t you think about what you were doing?” such as, maybe they have a family they have to provide for and they actually like the people they work with and what they do it’s just Jim from sales all of the sudden suggests a feature that’s unethical but the company believes it’s the thing to build... at some point, leadership should be blamed, not the engineer who just implemented it so they can go home to their spouse.

In software, there is incredible demand and engineers have a lot of negotiating power. So, we have the power to actually get new jobs easily!

And fine, but then when that horrible thing makes the news and their answer is "i don't care, i was just building the feature", I take that to be an extremely unsatisfactory answer.

And if they work at Facebook with those kind of unsatisfactory answers, they are probably very qualified for a lot of positions, and I don't think they'll be hurting for job offers elsewhere.

After all, they were just following orders.

How would it be illegal?

Doctors are often required to attest their ethics before doing a job.

But engineers are not. There are jurisdictions that this could be framed as discriminatory. Not in the US, but other markets.

I'm not sure why this would be discriminatory (in law or otherwise) for engineers and not for doctors.

Maybe the difference is that (computer-based) engineers are expected to do unethical work in some situations and for some employers, and there is an unwritten code that they can pass the buck and won't be penalised just for "doing their jobs".

What if the job they were "just" doing exists in a legal grey area? Or, more realistically, is flatout illegal?

You wouldn't hire a former prostitute who put themselves through education to better themselves and get a mainstream job?

Is the prostitution on their resume?

Whether what they were doing was "legal grey area" or "flatout illegal" is for the courts to decide, not for a random hiring manager/engineer interviewing that person. If you have a feeling that something could've been "flatout illegal", consider reporting them to the appropriate legal channels.

I, personally, would have done the latter in that scenario, but only if that entry was on their resume and they were proud of it. So no, I wouldn't report someone who personally confessed that many years ago they were dealing or doing sex work of the illegal kind. Though I heavily doubt that someone would be dumb enough to put it on their resume and advertise.