I couldn't resist playing with the numbers. A one megaton H-bomb equals the destruction of 46 grams of matter. According to this website http://www.biomedcentral.com/content/pdf/1471-2458-12-439.pdf the total human biomass is 287,000,000 tons. Destroying all that with antimatter would actually release the energy of twice that much matter. Doing a little math, this all equals 12 Billion H-bombs. That's like a hundred per square mile over the entire surface of the earth.
I wonder if any of these people every actually think about what they're saying.