Currently (until this bug) it’s supposed to trace back the call stack to the event that triggered it, and only allow it if the triggering event is something like a click. That’s what’s meant by “user gesture”, the opposite of code triggering it independently of the user.
“Consent” would be a positive acceptance in a browser controlled message box asking for permission to use the clipboard.
Most people agree that for copying to the clipboard the first is all that’s needed (there isn’t really a security concern here), for pasting from the clipboard the later is always required.
See the other discussion here: https://news.ycombinator.com/item?id=32614839
I would argue the actual vector is in the terminal, it should really validate the clipboard content.
Wow, rude.
One possible answer to your question: there is no way for a browser to detect "consent", which is a subtle and nuanced concept, but user gestures have a hard and fast definition, so that's the proxy they use.
The number of sites that reasonably need to know when I copy/paste or need to override what happens when I do that is approximately zero. There's no reason to allow it by default for all sites.