When a motivated malicious user (who doesn't actually need that much resources) will be able to convince people something is authentic because the verification passes when it shouldn't since naive users are primed to believe it by default.
Should we also abolish Pangram, because it's not 100% accurate? Someone might be convinced a text is not AI-generated when it actually is! We should get rid of it rather than fool people into thinking it can be determined accurately. What about antivirus? We should abolish it as well rather than fool people into thinking that their software is ever 100% safe. What about HTTPS? We shouldn't call it "secure" shell because the computer you're connecting to could be compromised! I could go on and on and on.
The median instance of AI image generation isn't evidence in a court case. It's cyberbullying, or deepfakes, or fake news. It's called "slop" because there's a lot of it being churned out at low effort.
Malicious users don't need to root their own phones. They just need to go to fakemyimage dot com, and someone else's rooted phone in a clickfarm-type setup signs it for them. I am not operating such a service myself because I thought it was unnecessary in making my point, but perhaps I will have to reconsider.