Whoosh. As opposed to 100 being boiling water? That works for science, but not humans.
Try to convey temperature to someone in a temperate climate, unfamiliar with any temperature scale. If you tell them 100 is the hottest summer day and 0 is the coldest winter one, they'll have a pretty good idea that halfway between, 50, is roughly the average temperature during spring and fall. They'll have an intuitive understanding of the scale, and be able to make reasonable estimates based solely on their experience.
Now tell them that 0 is where water freezes (good so far), and 100 is where water boils. What's the temperature half way in between in their experience? What would they guess the temperature to be on a hot day?
You're arguing that well defined scale points are needed, and they are for many things. But picking 0/100 vs 32/212 is just a choice - there's nothing inherently better or more accurate about the Celsius scale for scientific purposes. There is something better about the Fahrenheit scale for human purposes - it can work reasonably well without any instruments.