I disallow copying of copyrighted code into our product repositories unless the license is clear, I have even reached out to people to directly license copyrighted software, or for them to relicense their public AGPL/GPL license (for a fee).
To answer your statement directly:
1) StackOverflow submissions are CC-BY-SA, so if a person copies' code from there, even if it's copyrighted you can consider it good faith and remove the offending code from your product. This is actually a licensing nightmare but the current situation is the same as when the music industry accidentally uses an unlicensed sample and there's no current reason to consider it otherwise.
2) Github has a neat repository licensing feature (LICENSE) so you can easily tell what repo has what, not having a license file means the repository is fully copyrighted by default by the way; if we bundle GPL code then we would have to open source our game, which is not going to happen, so no you're not allowed to just copy code, but you can take inspiration; which is what Copilot is saying you should do in their terms *NOT COPY CODE VERBATIM*.
Ultimately: Software licensing is a joke to you because it doesn't really concern you, however it concerns me as it is quite literally part of my job to protect the company from being sued over doing something wrong here.