If a vampire came forward in real like, MTV would be all over them offering them a reality show. I would 100% believe that. Apart from that it's just seemed to me to be another metaphor, Vampires are huge at the moment, I was talking to a friend the other day who said they would love to be a vampire, and kept saying it over and over, plus the amount of people that actually believe they are vampires.
I think they took the vampire popularity and put the Buffyverse twist on it, in a world where vampires exist they are just as popular. People can't get enough.
If a vampire came forward in real life, people would react like they always do when they find out (or suspect) that there are people living among them who mean them harm. They would panic.
The police would suddenly have answers regarding all those unsolved killings of people with neck wounds, drained of blood.
They, and the federal government, would certainly react strongly to the sudden news that there's a whole population of monsters living among us, who look just like us and who use us as a source of food... and pretty much always killing us, at least until Harmony came along.
In the "Harmony Comes to the Nation" webcomic, Harmony openly admitted that vampires are evil and are compelled to kill people (saying that made them better than Slayers, since Slayers kill voluntarily). In the "Carpe Noctem" webcomic, we learn that some vampires are still going right ahead and killing their victims.
And religious groups... who hold quite a bit of political power and are not quiet about making their opinions known... would certainly have a problem with a species of self-admitted evil killer demons making themselves at home among us.
There might be a few cults of dumbasses, like in "Lie To Me," who think vampires are cool, but among the general populace the reaction would be panic, and among the people in power the reaction would be to take action against them.
The existence of the Initiative, as far back as season 4 and maybe earlier, proves that the government has known about vampires and demons for quite some time, and know what a threat they are.
There's a theory that human beings keep on making senseless war on each other, no matter how cultured and intelligent we become, because nature forces us to. It's a natural means of population control and a way of keeping us from getting too far ahead of ourselves. I would say that nature has been manipulating humanity regarding the vampires in much the same way. It's easier to exterminate us if we remain calm and apathetic and in denial about what's happening.