If God is against the death penalty why did He pay it for us?
"The soul that sinneth, it shall die."Only Jesus' death can pay for all the sins of mankind, whereas one's own death can only pay for one's sins individually.
— Ezekiel 18:4 and 18:20
"For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord."
— Romans 6:23