Brydo, it is nothing to do with belief, it is a fact that the Government , all governments , will have impact assessments on very many topics, including economics, supply chain, wars, natural disasters etc etc and as a Director of a Banking organisation, it was essential that I and my fellow directors were fully aware of the impact on the bank of different scenarios, both worst case, and best case, as well as everything in between.
Yellowhammer is acknowledged as the worst case impact of a no deal Brexit, on the U.K., but on the assumption that all scenarios will happen on day one, which of course they will not , in practice .
Your political leaning & background will dictate what you will chose to accept ,
But it will not change the facts.