As far as we are aware, no one ever doubted the existence and the danger of said disease at any occasion of its appearance, since it came and went for almost 500 years in Europe.

There were different interpretations as to why such a devasting outbreak had come into being, inevitably leading to some to believe it was a divine punishment for humanity's sins, a first swipe of destruction before the coming of Jesus and the apocalypse. I am inclined to interpret this tendency given the speculated death toll in the span of three years (1347-1350), speculated between the 75 and 200 milion people, possibly making up one third of the whole continent's population at that time.
We are told by chroniclers that people suddenly got ill, had very high fevers, chills, began vomiting and coughing blood alongside big, black buboes. Whole families could die in a matter of days, left in their homes until civil authorities managed to go get them, others wandered the streets and died huddled in corners, alone or with others. Occasions of cremation and mass graves were also discovered among various outbreaks, such as later oubreaks in Venice where two small islets were converted into leper colonies, where mass burials of plague victims treated with quicklime were found. Giovanni Boccaccio (1313-1375) recounts of the aforementioned outbreak of the XIV century in Florence, where within three days from the contagion, almost all, some even without fever, died. He also described its incredible infectivity by describing it akin to fire jumping on dry or oily wood.

It was perceived as the end of the world, and its damage could in no measure be negated.