Using AI to generate content isn't expressing yourself. It's expressing non-human AI content that's actually not a part of your self - AI content is the opposite of self-expression, it's other-expression. That's why people dislike seeing it peddled as self-expression.
You are missing the point, let's take "2001: A Space Odyssey" the novel book cover was not made by the writer Arthur C Clark. But by artist Robert McCall. Well not everyone can afford to hire an artist. You can be creative in your field, and still hire a human or use an AI to do art instead. What's the difference?
In traditional publishing publishers view the cover as a marketing tool - Arthur C Clark had negligible influence over what appeared on the covers of his books in his career when 2001 was released. That's not self-expression by any definition. You could hire a human to do art for you if you like, that's also not self-expression, nor is using an AI to do art for you. There's no meaningful self-expression in the act of having other people make things for you, they're doing the expression, you're enjoying (or not enjoying) the result.