Starting from the beginning,
Christ's death is indeed the sine qua non of salvation, but you could also just as easily leave "the sine qua non of" out of the equation. Christ's death is salvation, and I assert that Christ did not save all, nor did he do anything in his death other than save.
As to how what you wrote was a rebuttal to my invocation of justice, I have no idea.
Concerning the second part, the reprobate and the elect are both sinners, murderers and idolaters, thieves, liars, haters of all that is good and of righteousness and of God himself. This fact in and of itself is sufficient to make their damnation just regardless of anything else.
Now let's assume that God takes some of the people who deserve to die and pardons them. What you would have me believe is that now, as far as the other part are concerned, all of their sin doesn't matter anymore. You expunge them of all their guilt and reduce the justice of their damnation and their responsibility for their damnation to whether or not they have an equal shot at not being damned.
I suppose, in a sense, they had a shot at not being damned - they could have just been innocent all their lives. They didn't. No man ever has. No man ever could (save Christ) within orthodox Christian doctrine. And within orthodox Christian doctrine no man is with excuse. As such, with every man being born into the world a justly damned sinner, to say that any man has ever received an unfair shake is to accuse God of being an unrighteous judge.
Hence, if damnation be justice mercy may choose its own object.