Bombing a place of worship is just so unoriginal, and that also goes for the statements of "outrage" flying back and forth. For me, the heart of the matter lies in the more fundamental conjecture: if there was no organised religion, people wouldn't be sitting ducks in any church to begin with, whether it is a church in Jolo, a mosque, a synagogue or whatever the hell else people go to to "worship" and, as such, become targets for the zealous violence delivered by believers of other competing religions in the names of their respective gods.
Asking why there is such violence misses the point if the Why? question does not go deep into the question of why religions are made out to be such big deals to begin with. As such, any finger-pointing is pointless, because belief and senses of righteousness are always relative where religion is made out to be relevant. In discussions where religions are relevant; as such...
Christians will point accusing fingers at Muslims and Muslims will point accusing fingers at Christians.
Take out the concept of religion and the above sentence becomes meaningless -- and the violence that derived its perverted sense from it then disappears.
Anyone who openly practices their Christian faith in Muslim land to begin with is asking for trouble. One can, of course, argue that there must be no fear of open worship in a modern secular society such as ours. But such "musts" only exist in the empty promises of clerics and evangelists who routinely put at risk the lives of people they lead to believe are entitled to a foolish display of adherence to quaint religious rituals in an environment that is so obviously hostile to their belief system.
Are those who are maimed and killed in the name of their religion martyrs? Or are they just the unfortunate collateral damage routinely sustained in an ancient battle between narratives and their adherents, each claiming that theirs relates the exploits of humanity's sole legitimate supreme being?