> > That's part of why the apprentice period is so long.
  > I'm going to bet that technically, post-COVID, it's "$300 + few hours of videos and a quiz" long.

Try 5 years.

  > BTW. most contractors are in the "not very smart" group too

And that's why there's a code, and inspections, and penalties. They know that if they mess it up they could be fined, sued, or have their license pulled. Even with all their training they can still mess up. Which is why just giving a homeowner the electrical code and saying "good luck" is even less likely to work out. Many contractors learn just enough to do one specific kind of job, and then just keep doing that job. But they do learn the right way to do that one job.

  > Was I right to worry? Are they wrong? Well, I presume no to both, or else apartment building collapse would be daily news

Buildings are usually engineered so that if a single structural member fails the whole thing doesn't come crashing down, because sometimes shit happens. That doesn't mean it's a great idea to weaken the structural integrity of your house.

When it comes to putting a hole in a beam or column, it depends on the member, and there are specific sizes the hole can be, locations, etc. Sometimes contractors don't go into the details and say "it'll be fine", because the way they do it is fine, because they learned the right way a long time ago and don't tell you that part. They might even be dumb enough to not realize that you would do it a different/less-safe way. But they'd probably do it the right way themselves, because that's how they learned it.

However, buildings do fail on a daily basis. They just aren't news, or aren't catastrophic / life-threatening. A lot of bad stuff happens on a daily basis and almost none of it makes it into the news.