I think the people who pray a lot and the people who don’t pray at all often do the most good.   The people pray a lot prime themselves for action so even a materialist will see some effect of their prayer.  For example someone who prayed constantly for people affected by the Ebola epidemic probably would give money or service.  An atheist would put no stock in the efficacy of prayer and either take action or not.  It’s the lukewarm people in the middle that often do the worst, just praying a little and thinking that does a lot, an act of ease and convenience.  This group is what prayer shaming is aimed at.  If you really hate mass shootings you’ll do something about them besides praying.