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.
The thermal sensory system is extremely sensitive to very small changes in temperature and on the hairless skin at the base of the thumb, people can perceive a difference of 0.02-0.07 °C in the amplitudes of two cooling pulses or 0.03-0.09 °C of two warming pulses delivered to the hand.
https://biology.stackexchange.com/questions/30952/how-precisely-can-we-sense-temperature-differences