In the building case, you probably won't be the only set of eyes on it.
But to the greater point, I guess the ethical principle is don't do things that can put people at risk if you know you don't know what you're doing--much less put people at risk because you just don't care or want to take shortcuts.
If you think you know what you're doing but don't? I'm not sure how an ethics course or even a license is going to help there. Because you think you're doing things safely. Arguably, you're not even being unethical, just incompetent.
Now, a license is supposed to be something of a guarantee of a minimum level of competency. But it's pretty minimal. After all, it basically just means you do have an appropriate degree, have worked in the field under someone for a few years, and have passed some standardized test. All that suggests you know (or once knew) something about the basics, but not a lot more.
ADDED:
>However, that people aren't licensed EEs doesn't prevent them from tinkering with arduinos or SDRs; they simply can't sell their skills specifically as an electrical engineer.
In at least most states in the US, sure they can. (And in the ones that theoretically prohibit you from calling yourself an engineer if unlicensed, that's almost universally ignored.) I've known tons of people who have worked or work as electrical engineers and I'm sure few of them have PEs. You don't need a PE for most jobs. Though it's probably more common with civil engineering.