My whole point is clearly either being missed due to ignorance or a blatant refusal to believe the truth. The only "facts" about either serving someone copious amounts of alcohol, or seeing someone staggering around/vomiting etc, are that the person in question has been so observed. I'm not arguing about that, I too have seen many people being plied with alcohol, stumbling around, vomiting, lying in the gutter etc, and I have formed the opinion that they may be drunk.
But were I challenged to put my mortgage on that opinion being "fact", I could not honestly swear that they were indeed "drunk" simply as a result of what I'd seen. Yes, it's a strong possibility, but it is not something "proven", merely my opinion.
Hence the reason, for example, that Police Officers, who very often have to deal with alcohol related incidents, can only submit "evidence of opinion", therefore not absolute irrefutable facts, i.e. "I saw that the defendant's eyes were glazed, his breath smelled strongly of alcohol, and he was unsteady on his feet", etc etc.
It is then up to either the Magistrates / Judge etc to decide whether or not the submitted evidence is sufficient to prove the offence. That's why I or you as an eyewitness cannot prove a state of drunkenness per se simply by what we believe.