The main issue is that while you can use copilot to create "new"/transformative code, it's also trivial to get it to pump out licensed works in a form where you could claim "I didn't know it was taken from x project with y license because the tool made it for me".
I personally have no problem with copilot in concept however to do it (or any other AI model based text/graphics tool) without infringing on people's copyrights is practically an unsolved problem (excluding just per-licensing the training data ahead of time).