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.
I think we’re talking about two different issues here. The snotty attitude towards Jews doesn’t belong, in the first place. A “hardening in part” has come to Israel and that’s as far as we have any basis to speak of curses. We cannot prejudge what part. We don’t know for exactly what current Jewish nonbelievers Christ has effectually begged, and proper humility would tell us that a “damn those Jews” attitude just doesn’t fit. Also gentiles are partly hardened too. It’s not like God is frowning only at some Jews.
As for a funeral, since when did freedom of religion go away. One can express hopes the man has repented if it is unknown. To deem it a priori impossible for Christ to forgive that hideous murderer and pay for his sins demeans Christ who is infinite, not just a little figure on a cross.