I do not support this approach. At the heart of almost all religions is a belief in the love and forgiveness of God and in Christianity, a belief that even at the last minute the sinner may have seen the light and realised the wrongness of their actions.
IRA bombers were always granted catholic funerals.Sometimes, admittedly, they became ceremonies of glory and that I do think unacceptable, but I see no reason why these men should not be given a muslim funeral quietly, possibly at night, and their bodies consigned to unmarked graves. Many of these men have families who did not support them and tried to change them and funerals are as much for the living as for the dead.