As an American who's spent a lot of time outside the country this year, I've learned to love the metric system. Meters, liters, grams, bars–all really useful, logical, and simple to use. We should have switched a long time ago.1 2
However, there's one use of metric that I can't fully get behind and probably never will:
Using the Celcius scale to measure the Earth's ambient temperature.
Celcius is fantastic in the context of science and engineering, but it doesn't intuitively scale to the world's largest use case for temperature: talking about the weather.
Fahrenheit is far from perfect, but it's more human-centric since the scale is suited to our environment.
The Earth's usual, extreme temperatures are around 0°F and 100°F. Unless you live in the desert or the arctic, most temperatures you experience will fall somewhere in that scope.
You know that it feels uncomfortable toward both ends of the scale. You also know that you should take special precautions if you're experiencing temperatures outside of that range.
0-100° is much more intuitive than -18-38°.
Next, it's more precise; it expresses a wider range of temperatures without requiring a decimal. I don't care how engineering minded you are. Most people hate dealing with fractions of anything.
Between 0-100°F, there are only 56 degrees in Celcius. That's only a little over half as expressive using whole numbers.
Look at how much better Fahrenheit scales to the subjective experience of experiencing temperature on Earth:
|<0°||<-17.8°||Don't go outside.|
|0 - 10°||-17.8 - -12.2°||Break out your Canada Goose.|
|10 - 20°||-12.2 - -6.66°||Wear a coat to the frat party. It's getting serious.|
|20 - 30°||-6.66 - -1.11°||Scrape the frost off of your windshield in the morning.|
|30 - 40°||-1.11 - 4.44°||Yes! The first snow of the winter.|
|40 - 50°||4.44 - 10°||Perfect weather for a brisk fall day.|
|50 - 60°||10 - 15.55°||Comfortable, but wear a jacket (especially if you live in California).|
|60 - 70°||15.55 - 21.11°||Very comfortable, but may still be a bit cool for some.|
|70 - 80°||21.11 - 26.66°||T-shirt and shorts weather. Wonderful.|
|80 - 90°||26.66 - 32.22°||Incredible summer days...|
|90 - 100°||32.22 - 37.77°||Don't sit on black leather car seats.|
|>100°||>37.77°||It's hot enough that you could die if you're old and have no air conditioning.|
One of metric's strengths is not modifying units based on context. However, by using the Celsius scale to describe mainstream temperatures, the world selected standardization over convenience.
Metric fails here because it doesn't work for us; we're more important than the boiling point of water.
1 However, to the dismay of trolls everywhere, it doesn't matter that the USA doesn't use the metric system. All science and engineering work is already done in metric, and all food packaging is listed in both metric and imperial units. Local projects use the imperial system, and on a personal level, we use it for measurements like height and weight. In other words, it's not a huge impediment to continue using imperial, it's just an inconvienience for people who are used to metric when they visit the USA.
2 It turns out that we would have been one of the first countries to adopt metric: Thomas Jefferson ordered metric system documents from France, but the ship was attacked by pirates, so they never arrived. By the time the documents were requested again, Jefferson's influence was gone, so they were ignored.