[cpeterso]

The built-in dev tools are also a social-engineering attack vector. Try opening the dev tools on facebook.com and you'll see a huge warning to users that have been told to copy/paste malicious JavaScript into their dev tools. So one could make a reasonable argument that built-in dev tools are a bad thing.

[epoch1970]

Funnily enough, Facebook is one of the sites where I've seen these non-technical users have to use the dev tools to make the site usable again!

I think it was a login prompt overlay shown on business profile pages. These users didn't want to log in to Facebook, yet needed to view the business' Facebook page. The overlay would cover a significant portion of the page, without any good way to get rid of it. So the users would use the dev tools to clean up the page, essentially, even if they didn't really know what they were doing.