I agree with those who suggest that you can ethically take this person against his will, as being a threat to himself. In fact, I have in the past, contacted my resource hospital for their orders to do just exactly that in a medical run. The person was clearly in need of medical care, was anwering all questions clearly and correctly, yet was refusing transport. I contacted the resource hospital, either to document the refusal or better yet to get the order to transport against the subjects will. The ER Dr. agreed with my assessment that this person required medical care, and that refusal to seek it was tantamount to having an altered mental status and made the PT a threat to themself.
Of course, other systems rules and policies may, and probably will, vary.