I heard someone say that the reason why we don't see many instances of demonic possession today, like the wild man in the biblical account, is because most of the population has been baptized. As Christian influence diminishes in our society, as fewer people are baptized, and as more people dabble in the occult, we may see an increase in the number of these cases.
If legion lived in modern America, he would have been shot.
As far as demonic possession goes, I agree with Malachi Martin. It is the perfectly possessed who are the most dangerous. It is only in hindsight ,after they have done all the damage, they can do that they are recognizable.