Why did Ignatius of Antioch oppose Docetism?

Ignatius of Antioch opposed Docetism because the doctrine claimed that Christ possessed only a phantom body and that his Passion, death, and Resurrection were merely apparent rather than real.123

Ignatius insisted upon the reality of Christ’s human nature as a fundamental theological necessity. For Ignatius, the physical reality of Christ’s suffering and death served as a vital guarantee of "life everlasting" for believers. He believed that if Christ had died only in appearance, his own suffering and his willingness to face martyrdom for the sake of Christ would be rendered meaningless. By affirming the genuine humanity of Christ, Ignatius sought to protect the core of the Christian faith from the dualistic influence of Gnosticism, which viewed matter as inherently evil and therefore incompatible with the divine.321