Should a medical professional's conclusions be directly acceptable when it comes to fields related to material engineering? Usually no; the professional might be completely correct but due to the fact that they haven't studied engineering and is not a scholar in this area, their statements will be met with extreme scepticism and only after reviewing all the evidence and arguments provided in support for that particular conclusion, would the professional's conclusions be potentially in a position to be accepted. Most wouldn't bother with such, and simply ignore whatever the medical professional would have to say on the matter.
In the same way, since (as far as I know) Stephen Hawking was not an expert on religions, his arguments against God's existence should be individually reviewed instead of simply being directly accepted. Only then can a person be logically in a position to conclude whether the late physicist was absolutely correct or completely mistaken.
