My brother-in-law is an electrician, and he could tell you stories for days about the horrible and unsafe practices he sees nearly every day of the week in people's homes where they've done their own work.

Everything thinks they're smart, they can do things safely, etc., while only for a much smaller subset of people is that true.

I work with industrial electrical systems so I see a lot of how things are done "the right way". The amount of horrible bullshit that I've seen in houses that's been done by licensed electricians is staggering. I'd wager for every one dodgy install done by a DIYer, there's an entire house that's been wired in the laziest spaghetti style by a 17-year-old sparky's apprentice and ticked off without even eyeballing it by the main contractor.

A fun way to trigger a dumb argument is to say something about taping (or not) wire nuts.