I don’t mind when non-native speakers use it to express themselves, especially if disclaimed (but I give a pass even if not). Does it bother you?
Personally I would like people to try learning other languages more (it's hard but rewarding) but you can't learn every language ever, and it is really hard to learn a language to fluency.
Not all, but some machine translators can be comically (if not horrifically) bad sometimes. Search Twitter-become-X for examples. Native writers can't pick a working machine translator unless they are explicitly allowed to do so themselves.
But that a site might still want to discourage it, to avoid general degradation. It is a tradeoff.
If someone can write in the target language, just not well, a model could be asked to point out problems for the writer to fix. Rewrite a difficult sentence.
Ideally, I want the speaker’s words translated “verbatim” to English, to the extent possible.
It also points out the need for AI writing tools that very strictly just:
1. Point out misspellings and typos.
2. Point our grammar mistakes, if they confuse the point.
3. Point out weaknesses of argument, without injecting their own reasoning.
I.e. help "prompt" humans to improve their writing, without doing the improvement for them.
In fact, I would like a reliable version of that approach for many types of tasks where my creativity or thought processes are the point, and quality-control feedback (but not assistance), is helpful.
This is a mode where models could push humans to work harder, think deeper, without enabling us to slack off.