It's cool, I don't feel "attacked" by someone simply disagreeing. I just don't like dirty pool tactics when it comes to discussion and debate and then having those who pull them prance around proclaiming themselves "the winner" while stating falsehood about everyone else who has participated claiming they never brought anything to the table.
The discussion suffers from two issues here. First, anyone with a viable saving relationship with God prior to the Cross & Pentecost can easily be dismissed because they don't fulfill the literal criteria "spirit filled born again Christian" merely because no Christians existed prior to the Cross (or at least prior to Jesus' earthly ministry) and no spirit-filled ones existed prior to Pentecost.
I will of COURSE concede, and gladly so, that anyone walking in a vibrant, healthy relationship with Christ day by day, walking in the Spirit, living the abundant life in Him, does experience protection from that. No, they could NOT just overnight go from being in that experience to being riddled with invading devils or something.
My point, though, is that being born again and Spirit-filled today does not in and of itself guarantee tomorrow. Tomorrow one could fall away -- or be pulled down. Scripture talks about this life as a continual battle and that having done all we can do to STAND, we STAND. It doesn't even promise progress, we have to fight some days just to
retain the ground Christ gave us when we first came to Him! And to retain awareness of Him as the author and finisher of our faith, not we ourselves and not all our clever exploits. My point is this: it's a war. In war people get shot and crippled. They get maimed and EVEN KILLED. War has casualties. War has prisoners. War is dirty and does not play nice. And neither does the enemy.
The enemy does all he can to capture the citadels of mind, heart, and will in a person's life. His chief method for those of us protected in Christ is temptation. He can't just directly in one fell swoop grab us, invade us, and turn us from Christ into devil-worshiping demoniacs or something. Of course not. But he watches, waits, plots and bides his time. He will spend years picking at one sore spot until an infection develops and he will let it develop sloooowwwwly so that the person afflicted has no idea what's happening to them until it's too late. They keep doing what religion has taught them to do: blame themselves, flagellate themselves, berate themselves in secret for not ever being Good Enough or not being holy enough or obeying God enough or whatever it happens to be. They wonder why God isn't giving them power to overcome anymore, and think more praying will help, when in reality the attack is taking place on a deeper and more subtle level than just whether they give in TODAY to eating too many potato chips or having a peek at some naughty picture on the web, or

or whatever sin you want to insert here in our hypothetical scenario.
Since the day we come to Christ, things are no longer a sin issue, but a Son issue, but the enemy makes it a sin issue, constantly. The FALSE teachings done by "deliverance ministries" -- who are themselves confused about the nature of demonic infection and think it to be something we have to "sin our way into" -- provides a fabulous avenue for the enemy to continue twisting the knife in these wounds of guilt, failure, and self-recrimination. While the victim of his attack labors valiantly and fruitlessly to put out the fires that have been started, he's sneaking his Trojans in through the back door, so to speak. It's dirty pool and a total coup, but by then the footing of the valiant Christian soldier has been slipped enough to give him (the enemy) the advantage he seeks, and he doesn't stop until the one he's hassled, he can bring down entirely.
Again, stuff like that does not happen overnight. And doubtless long before the enemy's plan is complete, the individual in question would be doing and saying things that will cause those around him to judge that he has lost his hold on Christ somehow. He won't be
considered a viably born-again, Spirit-filled Christian anymore by the time it gets to the point of "inhabitation" ... and that he started out as one will be the subject of endless debate on the internet while he perishes for want of someone to just come along, reach inside as deep as those supernatural forces of evil have done, and rewire him to being his former self connected to Christ and hidden in Christ again, something he has lost the capacity to do for himself. That's what rescue is all about. That's what intervention is all about. That's what deliverance is all about.
And that's how a formerly born-again, Spirit-filled Christian can, in fact, become demonised.