It's not about plagiarizing. It's about needing to know whether you, not ChatGPT, can actually write well. How are you going to write original research? ChatGPT can maybe sort of help write your introduction, but it can't write about something you've just discovered. You have to know how to write or else you'll never be able to write anything original. Imagine how depressing the world will be when everything you read is just AI-mass-genersted pablum imitating and simulating human experience, but not truly connected to an actual person with real emotions.