Nobody has demonstrated that the universe must have come from nothing. If current beliefs, models and (fairly hefty) extrapolations are correct, then the universe may have come from nothing. However, (a) we have only fairly tenuous constructions to lead us to that hypothesis, so it could be found later to be wrong, and (b) Krauss's views on matter originating from vacuum fluctuations in physical fields don't really get us much further, for the reasons Yazata and I have given (i.e. physical fields =/= nothing). Nobody needs to be forced to take a stand on an esoteric thing like this, when so much is perforce unknown and probably unknowable. In my opinion a good scientist should be cautious here and talk only of models and possibilities. This is not a religion, demanding adherence to dogma from true believers.