You may be overstating that a bit. I've been doing tech for a while, and I can't recall anyone ever asking me to abuse my skills for ill-gotten gain.
A few years ago, a guy contacted me from HN, asking if I wanted to team up on some stuff. He sounded pretty convincing, and like an all-round decent guy.
For some reason, despite his likability, something seemed not quite right. I searched for a few variations on his name and email, and eventually stumbled across various reports of low-level frauds directly attributable to him. Really a very unpleasant individual, targeting the self-employed and taking them for ~$5,000 each.
If I'd spent less time researching, I'm certain two things would have happened:
1. He would've screwed me out of whatever agreement him and I came up with.
2. Whatever I worked on would have been used to defraud people one way or another.
When someone approaches you, it's not always immediately obvious that they're trying to do bad stuff.
EDIT: I'd nearly forgotten, a good few years ago, someone tried outright recruiting me for illegal work after seeing a LOOKING FOR WORK post I'd written here on HN.
Of all things, they asked me to hack some local authority's death records. Bless them, they'd taken the "hacker" part of Hacker News to be a literal news site for illegal hackers.
They went on to have a decent exit so that decision cost me roughly £1 million - I've never regretted it, I don't really have the temperament for a life of crime.... :-)
Funny enough, even the semi-technical ones are guilty of such requests too.
Over the course, I've learnt the hard way that saying no upfront is better than dealing with the fallout later
There are a lot of people interested that simply lack the technical insight to know exactly how to approach you or if what they want is even possible. If you are not the kind to boast about work at the pub, they will simply fail to find an opening that let them know: that their scheme is possible, that you can do it, and that you would do it.
Of course, I comes from a relatively bad area too. It is filled with people that share the spirit of Valley Startup Founders: nothing is ever really idle chat, every conversation is an opportunity and every minute must be productive. Their business model and area of expertise are a lot more shady though.
but I'm sure that's technically breaking some anti-spam law
Sometimes a matter of ethics can be reframed in the context of long-term reputational risk. "X bad incident related to our reputation" can be a lot easier to attach a dollar value to than "being unethical", and that is (in the end) what many engineer-employing companies care most about.
I've also told every company that has hired me, during the interview, that I refuse to do anything unethical. Of course they didn't bat an eye at it, but I wonder how many would have been surprised that I actually meant it and would stand up for it.