How could anyone harm people peacefully seating in a place of worship?

I doubt that these terrorists have read and understood Quran 22:40 :

" And were it not that Allah checks the people, some by means of others, there would have been demolished monasteries, churches, synagogues, and mosques in which the name of Allah is much mentioned. And Allah will surely support those who support Him. Indeed, Allah is Powerful and Exalted in Might."