I don't think it assumes that the secular-physicalist belief system has no meaning. I think I have argued quite clearly that this says there is and can be no meaning or purpose in a completely random, accidental universe, where everything happens according to fixed, but purposeless laws. What those espousing that belief have said, as I commented, is that this doesn't mean there is no meaning or purpose, it just means there is none inherent in this universe waiting to be discovered, but rather it is something that needs to be created. But, as the following comment suggests (and I agree) human-developed meaning and purpose is far from satisfying.