So unless I am a doctor I am obliged to call an ambulance every time I see a drunk person? The mind boggles.
Don't be silly that's not what I said, is it? And you well know it.
If a person appears to be severely incapacitated to the point they have lost control of their limbs, then I think it's fair to say that medical experience and expertise is very useful to have, especially if you don't know the person, what they've been drinking/taking or their medical history.
If the person may be at risk of harm, or harming others, then it's a job for the emergency services. That's their job.
It's about making an informed decision. You can't do that if you lack the relevant information. Better, perhaps, to involve those who may be better able to gain that information.
But you knew that. You're just being obtuse. 🙄
If someone is in such a state, on your premises, and you do nothing, you can be held liable if they die or suffer serious harm. Self inflicted or not. If they're out in a public place, then surely it's our civic duty to try and help?