Was Leo X right to condemn Luther's thesis that burning heretics is against the will of the Spirit?

I think it is probably good. In the Old Testament, any capital crime, such as adultery, homosexuality, or murder, was an occasion where the leaders of the congregation could take the life of the sinner, and the reason was divine: God wanted evil kept out of Israel, and said that if they let such people live, the land would vomit them out. We even see a form of this in Acts 5, where Ananias and Sapphira lie to Peter and drop dead, and in 1 Corinthians 11, where Paul says that because some abused the Eucharist, many are sick and have died, meaning God took their lives. So there was a continuing of the taking of life, but with God making the decision, and in Acts 5 with Peter making that civil judgment, backed by heaven, fulfilling Christ's promise that what Peter bound on earth would be bound in heaven. The question was what the Church would do with this prerogative to act both civilly and morally. At some point the Church decided it would be the spiritual determiner of a soul's state, and for capital crimes it would turn the person over to the king. In Israel there was a theocracy with no other nations to consider, but as the Church spread among the pagan nations, it had to adjust, excommunicating the unrepentant and letting the civil magistrate take its course. Leo X was right in the midst of that question of what the Church's responsibility was, and that is what he told Luther.