For the sake of the injured society

Desert is fairness as seen from God's perspective. 

Compensation might satisfy the injured party more than retaliation but lex talionis is what the monarch is obligated to prosecute, not for the sake of the injured party but for the sake of the injured society. The individual might well forgive the violation but the prosecutor must exact justice because the perpetrator deserves to get punished. 

Parshat Mishpatim is about what God needs to have happen, not what man has to do. God's participation in man's rule of law represents a perspective from which the administration of the law needs to be prosecuted. His presence in the matter is there to guide the ruler on the proper way to think about things.