Question: Why is it so hard to predict the future?
In the eighteen-sixties, the quickest, or at least the most popular, way to get around main cities such as New York and London was in a horse-drawn streetcar. Imagine, before the introduction of the automobile, horses were leaving about 2.5 million pounds of horse manure filled NYC streets per day. Think of the smell, the mess and the dead horses laying in the streets, moreover imagine the flies stopping by to take a rest and have a drink on your soup bowl.
Yes, it was understood that flies were a transmission vector for disease, and a public-health crisis seemed imminent.