You lost me there. I don't know that there are "basic flaws" on both sides of the argument. Both sides err when they insist their view is the only possible one and that anyone who disagrees simply does not understand the Bible, does not understand the grace of God, yada yada yada.
The very real problem with both sides of the debate is trying to justify the unjustifiable.
We have an inherent problem with the "flesh." That being, the Spirit is against and contrary to it. Gal. 5:17
It won't be saved. "Works" salvation folk believe their flesh isn't contrary to the Spirit and the Spirit against their flesh if they do "enough" sufficient works. Eternal security people refuse to see the same issues. And neither party really cares to connect sin to the devil, as scripture does. 1 John 3:8, Mark 4:15, etc.
So, who is the missing party in the conversations? Uh, yeah, our spiritual adversaries, as usual.
The spiritual reality IS that no believer really want's to fess up that their own sin is actually demonic. They can't make that statement of fact, because it is "personally" detestable to do so and demonic pride will not allow it to happen. So it's quite explainable.
The basic flaw on each side is dogmatism. There are two (more, actually) plausible views because there are ambiguities in the Bible verses.
I cited the easiest answer earlier in the thread. IF you (I believe you are somewhat of a legal expert) see the evidence, we might see that both eternal damnation and eternal salvation were walking in the same shoes, here:
2 Corinthians 12:
7 And lest
I should be exalted above measure through the abundance of the revelations, there was given to me a thorn in the flesh,
the messenger of Satan to buffet me, lest I should be exalted above measure.
There are two parties in the above shoes. Paul, eternally saved. The messenger of Satan, eternally damned.
Jesus makes the identical case in Mark 4:15 showing again, TWO parties.
Paul makes the identical case, again, in Romans 9:18-24. And again in 2 Tim. 2:20-21.
So, yeah, the answer is quite easy to see, but there IS another party who would prefer to see otherwise. Which is basically why very few can grasp the matters.
Are you suggesting God planted the ambiguities so controversies like this would arise?
We should recognize the deeper principles in play here. They would be for example Satan's moving into "actions" within MAN where the Word is sown. This is particularly true when it comes to LAW. Paul shows how this principle works in painstaking detail in Romans 7:7-13, proving that sin, which IS of the devil, 1 John 3:8, moves in antithetical fashions to Gods Laws, His Word. This is also why it's also basically impossible for anyone to be "legally compliant" to Gods Laws, because it's not dealing with "only" people, but also adverse spiritual agents.
Will these adverse spiritual agents EVER agree on anything? Uh, no. They like to keep us all in stitches with these stupid religious debates.
Or controversies like this arise because we are imperfect beings with imperfect understandings? Or the controversies are "thorns" that keep us from boasting? Your reference to 2 Corinthians 12 confuses me a bit. It seems like the ambiguities are precisely what give people a basis to boast - in effect saying, "Only I, not you, have the correct understanding." If you are saying we should remember that there are no obvious answers and that positions other than our own may have some merit, then this would be consistent with what I'm saying in the above paragraph.
I would merely point out that even with Paul there was an adverse spiritual agent who would never understand or agree on anything. And Paul at least recognized that fact for himself.
Few people understand how Paul could make the conclusion that he was the chief of sinners AFTER salvation. 1 Tim. 1:15. But if we observe his "against the Spirit" cohort in the flesh, the messenger of Satan, it's quite easy to see how he made that determination.
As it relates to this topic in particular, the blood of Jesus avails the messenger(s) of Satan in the flesh of man exactly nothing. Nada. Zilch. But for believers, yes, entirely forgiven. Two states of truth are seen again in this topic, simultaneously, but in opposition/contradiction.
And for the unbelievers, they are basically Divinely Intentionally blinded to the entire conversations, so it really wouldn't mean anything to them in their state of blindess. Acts 26:18, 2 Cor. 4:4, Eph. 2:2 shows them to be under the power of darkness, of Satan.