Hemant Mehta@hemantmehta Why would anyone #PrayforAmerica when it hasn't prevented any of the previous tragedies? America needs people who can take action, not God.11:56 PM - 7 Jul 2016
Mehta seems to have quite a following in secular circles, yet this is such a dumb objection. Consider those science fiction scenarios in which a time-traveler goes back in time to change the past to avert a future tragedy. A side-effect of his success is that when he instantly returns to his own time, he has no recollection of what he did. By producing a new timeline, his action erases all evidence of the old timeline. No one remembers that past because that past never happened in the new timeline in which they now exist. There's nothing for them to remember.
God preempting a tragedy is similar to that except it doesn't suffer from time-travel antinomies, inasmuch as the tragedy never happened in the first place. So how would Mehta be in any position to know that God hasn't prevented any previous tragedies, in answer to prayer.