The idea of a vulnerable adult is a little vague. Are you concerned with mentally challenged, handicapped, drug abusers, alcoholics or other.
Do you have an example to which a more suitable answer could be given? Do you want to give an example?
The notion of a vulnerable adult seems to only arise when that person is charged with a crime.
Take for instance the recent events where a young man with a low mental age was coerced into attempting to suicide bomb a restaurant. He in fact managed only to explode the detonator in the toilet, wounding only himself and scaring the life out of the restaurants customers.
Was he guilty of the crime, most definitley, was he capable of planning this event, most likley not, was he coerced, most likley.
The problem comes when you look closley at the history of this individual and the problems he has had growing up. It becomes harder to treat this person as an actual criminal and more of a victim. He is not capable of reasoned thought above that of a 7 year old, he is easily manipulated, and on the whole, pretty stupid. Our concerns are now for this person, how he was so easily controlled. The answers to these questions place this categorize this person as a vulnerable adult. Unfortuatley for all concerned, it is rather too late!
A vulnerable adult will most likley have been a vulnerable infant to begin with. A good home, solid education and firm moral teachings are luxuries of the intelligent and as I have said on other responses, you have to start good to get good. A child who has low intelligence requires greater attention, better guidance. If it is not available to them, what chance do they have.
If you are looking to dig deeper on this subject, then your local police would be happy to discuss the issues and legislation . They would be able to offer information about how a young adult would be treated under certain circumstances and you could offer the example you have on your mind, rather than let everyone here on Answers know.
After all that, have I helped?