Hey Bill...
One of the reasons I believe what I do actually resides in that very passage. In verse 12 it states...
12For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.
High places there is also translated "the heavenly relm". I do believe that one day we will come face to face with demons and preparation begins during our time here on earth.
The evil of this world is simply the wickedness of man. When humans chose the wrong path, evil gets a tighter hold on society...whether that is this state, this country, or the entire world. The evil is of Satan, but I don't believe he or any of his crew resides here on earth causing any of the havoc. Unfortunately, we humans don't really need that assistance.
Also, I don't think that anyone can be possessed now. That goes back to my problem with scapegoating. We either choose to accept Christ or reject Christ...Demons don't whisper in our ear and get us to do bad things, nor do they take over the bodies of anyone and make them do anything. We choose our own paths, and to say that a demon can come in and choose the path for a human goes against that thinking. Faith in Christ is key. If someone chooses not to put their faith in Him, they'll be kickin it with the demons soon enough. To give anyone the scapegoat of "the devil made me do it" by way of demon possession takes away free will to make that choice.