Ugh. Although I think there's some good solid advice in there, the whole tone of that article really irks me. As someone who actually works with people with all types of personality disorders, addictions and mental problems every day, I find it a bit tiresome that someone would put together a guide that is essentially rephrasing over and over again "bad people are bad! Don't associate with bad people!".
Actually, if you want to preach about correct behaviour, why not just stick to your own? Know yourself, know your boundaries, and learn from your mistakes... "leeches" and "vampires" don't just come along one day and steal something from you... you play an active part.
The person may be be struggling with a serious problem, but that is nobody's business but theirs. If you wind up in a relationship in which you tolerate bad behaviour from them, or even encourage it, then you are just as responsible, and it is up to you to remove yourself. If you don't, it's not because of the inherent badness of a "problem person" but because your interaction, your relationship, the thing that you produce jointly, is unhealthy.
Making an endless list with every second bullet point starting with "beware" actually seems unhealthy to me. Why categorize people into different groups according the harm you are terrified they might bring into your life? Why not a list on how to strengthen your own awareness of yourself and how you relate to others, and a little more compassion for people who are struggling...?