dafman:
From what I can see, there is nothing to stop an iPhone user using Airtags to secretly track an non-iPhone user without their knowledge.
Once on the market, if these things really take off, Airtags may actually be an effective Trojan horse* for moving people across to the iPhone ecosystem solely for the piece of mind of having protection from being tracked without their knowledge.
According to this article the Airtags are designed to make a noise when they are moved after being separated from their associated iPhone for a period of time. So, I think that would mitigate the scenario that you've described.
I am usually very critical of big tech companies for thrusting products into the market without properly thinking through the real world applications of the product, but in this case I am pleasantly surprised to see that Apple appears to have given a lot of consideration to the potential misuse of Airtags. Domestic abuse is something that the general public are quite rightly very concerned about, and this is a really good example of why tech companies need to consider social issues as part of their product design lifecycle.