Why we have a moral responsibility not to criticize praying

I doubt any of those benefits are specific to prayer as opposed to meditation. I'm generally not opposed to prayer in cases where there's nothing practical that one can do (like donating money or time/effort to a cause). It certainly doesn't follow that just because prayer has some benefits (that, again, may not be different than meditation) that we have a moral responsibility not to criticize a belief in God. In order to argue that you'd have to show that the negatives of such a belief outweigh the positives, and good luck with that.