It was written to Jews who had converted to Christianity and were under intense pressure to go back under the Law. Everything in the letter has to be read from that perspective.
Those who relied on the daily sacrifice instead of invoking 1 John 1:9 (confessing directly to God) were in effect crucifying the Lord all over again, since He is the Lamb of God who takes away the sin of the world. The daily sacrifice was a foreshadowing of Him, and when He came the shadow gave way to the reality. The old way was no longer sufficient to restore them to fellowship (Hebr. 10:1-18).
“Those who relied on the daily sacrifice instead of invoking 1 John 1:9 (confessing directly to God) were in effect crucifying the Lord all over again...”
There is no hint in the letter that he is discussing people currently offering blood sacrifices while calling themselves Christians. He points out the superiority of Christ to Old Testament law, but ANYONE trusting in animal sacrifice INSTEAD of Christ would have been condemned outright and vehemently.
“It was written to Jews who had converted to Christianity and were under intense pressure to go back under the Law.”
If they went back under the Law after having converted, then they would be doing what you say is impossible. They would have been converts who then rejected Jesus Christ, and your argument is that NO CHRISTIAN CAN EVER DO SO.