I don't think I can tell the difference if something is only one degree apart in Celcius, let alone Fahrenheit.

Comparing an 18C day to a 19C day, for example, I challenge anyone to notice a difference. A 64F to 65F day? Good luck.

I agree with the Celsius scale making sense around zero. Water freezing is probably one of the most relatable, quantifiable examples of a temperature point for the most humans. However, lots of people don't live somewhere that it snows, or even own a freezer.

So what's the most common touch point for people? I'd go with water boiling. I can't really think of what sort of person who did not have exposure to that at some point. That should be the zero point, the common denominator.