My sources identify Psalm 90 as the only one thought to be written by Moses. Not that it really matters, the authorship of most of them can't be definitively established anyway. Most are traditionally attributed to David, possibly because they were clearly meant to be sung or chanted and David was reportedly a skilled musician. All very interesting, and fertile ground for speculation, but it doesn't address the obvious absurdity of the claim in the bits you cited from Psalm 91. I've read interpretations of it that suggest it means nothing bad will happen to you except what god chooses to inflict on you, which I don't think is an improvement. I think I'd vote with French Patriot here, much of Christian dogma seems to me to be an invitation to slavery, what Christopher Hitchens labelled the "celestial dictatorship." No thanks.