Ah, so disagreement with Giuseppe = "intellectual dishonesty", and silence = some sort of concession of the point. I know this game
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Paul regularly quotes 'scripture' out of context. The quotation you think is interpolation is simply Paul clarifying what scriptural curse he believes Jesus to have come under, after having said that Jesus became a curse for the faithful. There's no tension with 1 Cor 1:22-24. It simply makes sense if Paul is thinking of a Jesus crucified here on Earth (as this Jesus is thought to have attained a curse originally prescribed for Earth-bound pre-Israelites under the Mosaic Law). There is no manuscript attestation in favor of interpolation, and (as far as I'm aware), there are no Church Fathers who speak of it ever having been found omitted. According to BeDuhn's reconstruction, the phrase is present in the Marcionite Apostolikon. Surely the tendency of Marcion was to distance Jesus from the OT, not interpolate more OT scriptural allusion! Your argument for interpolation is extremely weak, if not completely non-existent outside of your searching for a reason to get around yet another otherwise obvious 'Earthly-Jesus' reference in the undisputed Pauline corpus of the sort that Carrier-schoolers regularly assert don't exist.
Re: Hebrews 13:
Simply read a verse earlier:
the bodies of those animals whose blood is brought into the sanctuary by the high priest as a sacrifice for sin are burned outside the camp. Therefore Jesus also suffered outside the city gate in order to sanctify the people by his own blood
On the literal level, the author appears to be showing his awareness of the gospel Passion Narrative, where Jesus is crucified just outside the walls of Jerusalem. On the allegorical level, the author appears to be referring to his "outside" of the heavenly tent - i.e. down here on Earth among us wretched lot!
When the author writes...
Let us, then, go to him outside the camp, bearing the disgrace he bore, for here we do not have an enduring city
... It's just another poetic way of saying "take up your cross".
Hebrews is littered with 'Earthly-Jesus'. The author seems aware of the Gethsemene scene (probably from the gospels, I would guess), describing Jesus' "days of his flesh" when he "offered up prayers and supplications, with loud cries and tears". The author describes Jesus as from the "tribe of Judah" without clarifying that he doesn't mean the earthly-tribe as such a phrase would be most naturally heard. The author likens Jesus to us Earth-bound humans "in every respect", "sharing in flesh and blood". The author quotes the scriptural phrase "made a little lower than the angels" to refer to mortal Earth-bound humans before quickly applying it to Jesus also, thus suggesting equivalence. The author understands Jesus as having called Earth-bound humans his "brothers". Jesus' sacrifice is believed by the author to atone for Earth-bound human shortcomings. It "sanctifies the people". How? Apparently because Jesus was "like them in every respect". This Jesus "came" to "help the [spiritual] descendants of Abraham", etc. The author's atonement logic makes very little sense if he is thinking of a Jesus crucified somewhere else
other than here on Earth, alongside mortals and as one of us.
You also haven't addressed the issue that the author of Hebrews is probably not the same as that of Galatians (nor 1 Thessalonians). So assuming a consistency of theology between them is risky.
My study list: https://www.facebook.com/notes/scott-bignell/judeo-christian-origins-bibliography/851830651507208