How are you going to say that the Old Testament doesn't permit anyone to die for you if God actually calls us to acts with sacrificial love. Why is Jesus not a valid offering for all of mankind? He was absolutely perfect and he sacrificed Himself willingly. That's all that is needed to wipe away our sin. The lambs the Israelites sacrificed in the OT were unblemished, just like Jesus. And I do not believe that communion is the same as drinking blood. I don't know how you got the idea that I did, but I am sorry for any confusion I may have caused.
As for sin also being against humans, Jesus said, "What you do to the least of your brothers, you do to Me." So, even if it is against a human, it is also against God.
Also, Exodus 23:7 is talking about the justice system for Israel, not the sacrifice system, as you seem to have taken it.