About three times as many people speak English as a second/foreign language compared to native speakers, not to mention people with no English fluency at all. That's a lot of people who might use an AI writing assistant for legitimate reasons that go beyond poor character. Same as we might do if we needed to communicate in Farsi or whatever.

It seems better for people to simply write in their native tongue. By translating what you write before sharing it, you are robbing readers from the opportunity of using future, better translation technology. It freezes text at the current capabilities of translation software. It also drives us towards a monolonguistic world, and I think a lot would be lost in that (said as a monolonguistic English speaker).