@razmee209: Fair enough, it is not marketed as being a theft protection (although I believe it to be a common use case) but after some research I can see how such a device could be abused.
The comparison falls behind though. Because no, car alarms are present, thieves are aware of them, they are not meant to secretly inform the owner. They are meant to avoid break-ins by raising attention (something a thief does not want). Think of it as a silent alarm on your property. A siren might raise awareness and burglars will leave with everything they have so far. A silent alarm will give the owner the opportunity to call the police and catch them in the act. So if the AirTag alarm would be at a sound-level were it would raise a lot of attention, then yes it could be a good thing (also in sense of abusing the device) but a quiet chirp that only makes a thief aware that he is being tracked by the owner - not so much I feel like.