And the physiological discussion concerning the Son of God in the Timæus of Plato, where he says, He placed him crosswise in the universe, he borrowed in like manner from Moses; for in the writings of Moses it is related how at that time, when the Israelites went out of Egypt and were in the wilderness, they fell in with poisonous beasts, both vipers and asps, and every kind of serpent, which slew the people; and that Moses, by the inspiration and influence of God, took brass, and made it into the figure of a cross, and set it in the holy tabernacle, and said to the people, If you look to this figure, and believe, you shall be saved thereby. Numbers 21:8 And when this was done, it is recorded that the serpents died, and it is handed down that the people thus escaped death. Which things Plato reading, and not accurately understanding, and not apprehending that it was the figure of the cross, but taking it to be a placing crosswise, he said that the power next to the first God was placed crosswise in the universe. And as to his speaking of a third, he did this because he read, as we said above, that which was spoken by Moses, that the Spirit of God moved over the waters. For he gives the second place to the Logos which is with God, who he said was placed crosswise in the universe; and the third place to the Spirit who was said to be borne upon the water, saying, And the third around the third. And hear how the Spirit of prophecy signified through Moses that there should be a conflagration. He spoke thus: Everlasting fire shall descend, and shall devour to the pit beneath. Deuteronomy 32:22 It is not, then, that we hold the same opinions as others, but that all speak in imitation of ours. Among us these things can be heard and learned from persons who do not even know the forms of the letters, who are uneducated and barbarous in speech, though wise and believing in mind; some, indeed, even maimed and deprived of eyesight; so that you may understand that these things are not the effect of human wisdom, but are uttered by the power of God.
http://www.newadvent.org/fathers/0126.htm
Who is for Plato "he" who placed him crosswise in the universe"? Surely the Platonic demiurge (not an evil being).
This Platonic demiurge is for Justin allegorized by the Moses (and by the God of Moses) while the crucified Son would be allegorized by the impaled Serpent.
So Justin is replying against the accusation raised by the his enemies. The Christians like Justin are accused of believing in a celestial crucifixion of Jesus just as other Christians. Justin denies this, by answering that "all speak in imitation of ours": it is not him who is euhemerizing the celestial crucifixion by introducing a Gospel Jesus, but it is them (probably a group of rival Christians) who, like the "Christian" Plato did in the past, are speaking now about a celestial crucifixion in mere imitation (co-optation) of the historical crucifixion of Jesus of Nazareth.
I think and believe that this passage of Justin is evidence of the contrast between "mythicist" Christians (believing, like the "Christian" Plato, that the Son of God was crucified in heaven) and historicist Christians.