Sure but then they would have to explain why, if there was no loss or gain, how it could have been a sacrifice without a loss or gain.According to Christians, who believe in the trinity, God did "step up himself", as his incarnate form of Jesus.
Tell us how you can sacrifice something to yourself.
You assume a very specific interpretation of how "salvation" comes about.
Jesus' death and resurrection underpin a variety of theological interpretations as to how salvation is granted to humanity. These interpretations vary widely in how much emphasis they place on the death of Jesus as compared to his words.
...
Among Eastern Orthodox Christians, another common view is Christus Victor. This holds that Jesus was sent by God to defeat death and Satan. Because of his perfection, voluntary death, and Resurrection, Jesus defeated Satan and death, and arose victorious. Therefore, humanity was no longer bound in sin, but was free to rejoin God through faith in Jesus. - http://en.wikipedia.org/wiki/Crucifixion_of_Jesus#Atonement
...
Among Eastern Orthodox Christians, another common view is Christus Victor. This holds that Jesus was sent by God to defeat death and Satan. Because of his perfection, voluntary death, and Resurrection, Jesus defeated Satan and death, and arose victorious. Therefore, humanity was no longer bound in sin, but was free to rejoin God through faith in Jesus. - http://en.wikipedia.org/wiki/Crucifixion_of_Jesus#Atonement
Those who emphasize his death typically also emphasize his human aspect, i.e. free will, as an example of how man could freely follow God's will. Jesus knew and prophesied his own death, so he was free to avoid it.