And anyhow. If whatever Christian group bid him farewell to eternity had any class, they’d do what Christ did. Pray for the forgiveness of all sinners.
During the Middle Ages, the Church promulgated the concept that, even in war, there were rules of decent behavior that had to be followed. The Church generally didn't have the power to directly enforce such rules, but they did have ways of exerting pressure -- such as denying particularly flagrant violators the privileges of funeral rites and burial in consecrated ground.
Undermining this precedent is a serious offense by these schismatics.