Why do muslims believe their sins can paid for by the unbeliever? The unbelievers blood is sinful. God is perfect. Is this not mocking God?

God is perfect therefore the sacrifice must be perfect as God is a perfect and righteous Judge and the sin must be paid for perfectly or the God in question is not a God because God has no blemish, stain or mark and to stand before him in judgment without absolute assurance of sin being perfectly dealt with would be very dangerous and the most serious eternal risk any person would and can ever take. For example : Our sin is not judged but the actual person who is a sinner, the sins committed are a by-product of being a sinner therefore we cannot seperate the sins from the sinner. The sin can be forgiven but the sinner remains a sinner and to stand before a perfect God would be like placing petrol covered rag in front of a blazing pure and perfect eternal clean and pure fire. Surely God perfect standard is to be kept, never would God who is perfect lower his perfect standard to accomodate mere sinners as this would be God becoming less than who he is - perfect. God must and cannot compromise in the slightest or all sinners by nature would behave in every evil way excusing all types of evils and transgressions based on faulty scales of judgment and justice then take a huge risk going to judgment before the most righteous and pure living God. This is a major problem for all men whatever religion, ideology or belief they adhere to. God must be perfectly satisfied based upon who he actually really is , a perfect righteous judge who is God.