How is that different to the current situation where I can view my wife’s location via her phone?Certainly would be a security issue. It'd allow you to avoid the security measures in place to prevent people tracking others without them knowing. Put one on the wife, set it to be "hers" so that her iPhone doesn't alert her when it's nearby, then Family Sharing it to you so that you can view the location.
If someone can get hold of their partners phone to allow sharing of the airtag then they could just have easily done that for their phone or watch ages ago.
This is where the security comments don’t make sense to me. Family sharing already shared the location of your phone and other devices. If security is an issue for airtags then why is it ok for the other devices.