Stross makes a few different claims, but they don't seem to add up to any kind of substantial critique of singularity-belief. The simulation argument is just a tangent: it doesn't actually have anything to do with the probability of a technological singularity. He basically says he doesn't think uploading is likely and then describes why it is undesirable anyway.

The argument that religious opposition to uploading will prevent it from being introduced is parochial, since there are huge countries like Korea, China, and Japan which are overwhelmingly secular, and where the technology could very plausibly be developed. In addition, secularism is increasingly dominant in North America and Europe, so that viewpoint is short-sighted as well. More to the point, I sincerely doubt religious people would really have a problem with (other people) uploading in the first place. Stross's view that people would launch holy wars against uploaders seems like paranoia to me.