If you need to go through the suggested code to ensure it's correct, you may as well write it yourself?
If you glance at it and it looks about right, you can potentially overlook bugs or edge cases, you'll lose confidence in your own code since you didn't properly conceptualise it yourself.
Potentially for newer developers it robs them of active experience of writing code.
Much like learning an instrument, improvisation, or say physics, a lot of people learn by doing it, even if it's grunt work. IMO this is necessary for any professional.
Maybe it will be seen as a crutch, maybe I'm getting old? I have tons of code snippets, but it's usually stuff I've written and understood and battle tested, even if it was initially sourced from SO. Having it in the text editor and appear out of nowhere with no context seems like it'd need some adjustment in apprehension.
Edit: I should have been clear, I'm not against others using Copilot and will try it out myself. I can see it being useful in replacing one-line libs like in nodejs, i.e., copying a useful well-known and needed snippet vs installing yet another lib that could be a sec issue.
Also the industry is the real gatekeeper—we have tools that don't require us to repeat prior-art, yet have to go through hurdles of leetcode-style interviews for a job. Maybe in the future the hardest part of being a (AI-driven) developer will be getting a job?