Another thought on the atonement

Every student of scripture knows that Hebrews 6 is one of those few very difficult passages of the New Testament to interpret. The author, whoever it may be, of this book writes "Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God, and of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment. And this we will do if God permits. For it is impossible, in the case of those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit, and have tasted the goodness of the word of God and the powers of the age to come, and then have fallen away, to restore them again to repentance" (Hebrews 6:1-6)
Affirming the Calvinistic doctrine of Perseverance, the reformed interpreter often views this passage as referring to unbelievers. These are Jews who entered into the Christian community, yet have not truly been regenerated, who are leaving the church to go back to Judaism under persecution. Thus, they are non-elect people. They were never truly saved in the first place.
My question is not about the issue of apostasy in this passage, which certainly is hard to deal with, but with what the author says at the end of this discussion, "they are crucifying once again the Son of God to their own harm and holding him up to contempt." If this passage is dealing with unbelievers, it is implying that Christ has already died once for them. How does one who takes this interpretation deal with that?
This is by no means a definitive argument against limited atonement; I am simply pointing out that certain interpretations of the apostasy idea of the passage necessitate a universal atonement. Many do of course take the hypothetical view of the passage which avoids the problem altogether.