Most people are bad at writing. This will make them "better" at writing, but only in a certain way. I love reading things people write, because it gives me a window into their mind, how they think, who they are at a deep level. That is the joy of reading, and the structure of writing is a big part of that.
Now, a lot of people's writing has become homogenized by the computerization of our world already, but only at a low level: spelling, basic grammar, and so on.
When people have the ability to inpaint whole paragraphs, dreamed from the blob of internet text (which is mostly corporatized, computerized, email-ized, sterile in the way described above) we will lose something essential.
And another problem arises. I send an email asking something, to a coworker or to a friend. They inpainted their response. Did they really understand what I was asking? Did we really communicate at all?
Images, I guess, suffer from the same problem. But images are less interpersonal. They are communication, but not communication like writing is communication. In nearly all circumstances, images are less subtle than words are (the subtlety of visual communication happens irl, where such machines have yet to insert themselves).