Final answer:
Mr. Otis says 'I don't believe in ghosts' because he is a practical man who puts his faith in facts and logic rather than superstition.
Step-by-step explanation:
In the story provided, the character Mr. Otis says 'I don't believe in ghosts' because he is a practical man who puts his faith in facts and logic rather than superstition. He scoffs at supernatural beliefs and believes that everything can be explained scientifically. This is evident in the text where it states 'John is practical in the extreme.
He has no patience with faith, an intense horror of superstition, and he scoffs openly at any talk of things not to be felt and seen and put down in figures.' So, Mr. Otis's disbelief in ghosts is based on his rational and scientific mindset.