He has the only TV Tropes page with a title in SCREAMING CAPS!
In the Northeastern part of the United States, it is approximately 100* F on the hottest day of the year, and 0* F on the coldest day. Thus it is intuitively easy to compare how hot or cold it is from day to day, or year to year.
Perhaps in slightly warmer areas, 0* C is the coldest day of the year, and thus feels just as intuitive. However, this still leave the hottest days of the year around 40* C, which isn’t as impressive as nice round 100* F.
Now, the mile is a nice, intuitive unit of distance. As my username might suggest, I am an avid runner. On a long distance run, I can easily and accurately measure the distance I covered by looking at my watch; I consistently run an average of a 10 minute mile. I assume that the distance was standardized based on centuries of people having similar running times.
In kilometers, I might be able to get a good estimate my using 1.5 km per 10 minutes, or 10 km per hour, but after running half my life, why am I going to bother?
What we need is to establish the metric league. At 5Km, it would be consonant with the traditional league (which was a rough measure anyway), and it would sound so cool.
Similarly, the foot is a very convenient measure. A good number of people have shoes exactly, or nearly exactly, one foot in length. Need to estimate the length of a room? Walk toe-to-heal from wall to walk. Need to check if a car can fit though a gate? Walk toe-to-heal in front of the car. You almost always walk around with an accurate measuring device!
12 inches to the foot, however; no idea :shrug:. You could think Subway and cut a 12" sandwich into two 6", three 4", or four 3" sandwiches; but you could just as easily have 15 cm, 10 cm, or 7 cm sandwiches. Even I can’t defend the lowly inch. 
And each section being divisible into 640 acres, this is why parcels of farm land often occur in multiples of 40 acres, and also why we hear about the ‘back 40’ or ‘east 80’ in rural contexts.
These are all mostly theoretical instead of actual problems, except for number five. That has nothing to do with a given system of measurement but with someone writing down a recipe incorrectly, if they wrote it down in Imperial Units you’d have just used those and gotten the correct output, if they wrote it down in U.S. Customary Units you’d have been able to try that and gotten the correct output. The fact that you claim neither works is evidence the person who wrote the recipe down did so incorrectly.
There are people to whom the answers to the first four questions are important, and by and large they will know exactly how to solve those problems by heart. My grandmother I would bet my life could tell you exactly how to go from teaspoons to tablespoons to cups to quarts to pints or whatever (were she still alive, obviously.) Obviously Americans cook food all the time without it all collapsing into an apocalyptic mess, so even the ones who don’t know how to do conversions apparently tough through it somehow.
None of this is me making an argument in favor of changing or not changing. But none of your “problems” have been a big enough deal in people’s lives to change our system of measurement. Plus, and most importantly, there is no law against using metric. And it makes no real sense to pass a law mandating its use. Anyone in America who wants to is free to use metric for every problem you listed, you can easily buy metric measuring cups, use metric measures to do your fish tank volume calculation or etc. In the construction trades one can’t as easily switch due to limitations on materials, but if there were significant customer demand the trades would change on their own.
What we’d end up with is a system where the people who really feel they need to use the metric system would use it, and the people whose daily lives are genuinely not meaningfully impacted by any of the “problems” with U.S. customary units would go on using them. And that’s actually pretty much exactly the state as it is now in the United States.
You make a point as to why we don’t really need any legislative change, though. Where economics or practical concerns have made SI more appropriate we’ve been using it–since at least the Apollo program as you mention (and long before of course), that’s still not a compelling reason why it helps anyone or society for me to think that it’s ~14mi to my work from my house or ~22km. I don’t know the exact distance nor do I need to, I just know it roughly and that’s close enough that I could tell someone and they can easily picture how far away it is. Neither metric or U.S. customary is better there. Nor does anything you say provide any meaningful reason for me to think of my personal weight or the weight of various objects in kg instead of pounds.
You’ve made a good argument for use of SI measurements in a few places, and that sounds like the people who do that kind of work should use that system–and it appears they do. Has nothing to do with anyone’s day to day use of the measurement system though. Large swathes of the population in fact don’t often need to measure things using a measurement system at all.
You’re confusing decimal and metric. There is nothing about the British currency system that was synonymous with “Imperial” measurement system used in the UK before they switched to metric nor is there anything inherently metric about dividing a dollar into 100 cents.
Might as well point to our 12 hour clock if you want to make the same point in reverse, why not divide day into a base 10 unit? There’s a reason when they invented the metric system they looked at dividing the day into base-10 and other types of units and mostly decided not to (the modern metric system does incorporate decimal divisions of seconds, but has no unit for time greater than the second.)
Even people that use the metric system don’t use it right, so why should I bother to change?
I mean, how far is the earth from the sun in metric? If you said 149,600,000 km, congrats, you just used the metric system wrong. If you actually used it right, it would no longer be kilometers when the number is that big. For large distances you should go through megameters, gigameters, terameters, etc, but no, you just stick with kilometer making the whole thing pointless. Why even bother with kilometer, just stick with fugging meters and call it 149,600,000,000 m. Or better yet, just forget the whole thing.
You don’t believe a base-10 currency is used for the same reason a base-10 measuring system is?
Because God didn’t make the day 20 hours, the moon travel around Earth in 30 days, and the Earth’s orbit around the sun 300 days. He’s not a base-10 kinda guy.
Then how come people don’t resist change when it’s for the worse? Which happens every day.
I am thinking that they just stick to kilometers because that’s what everyone is familiar with (driving, walking, etc.). Most people are familiar with how far something is in kilometers so they just leave even very large measurements in kilometers so it’s quicker to understand “how far” that is. Now, putting it gigameters, while easy to calculate, would make people actually have to do the conversion of putting it into kilometers so they can better understand how far that actually is. To avoid this inconvenience, they just mention it in kilometers.
The ancient Romans, building on the measurement units of the ancient Greeks, measured long distances in Stadia, where one Stadion was 600 (ancient Greek) feet.
Given the difference between their feet and modern feet, one Stadion works out to about 1/10 of a modern statute mile.
And before you go around saying “Aha! I knew it! A Stadion was chosen because it was the distance a jogger could run in one minute!”, I hasten to remind you that the ancient Greeks did not carry stopwatches, and even large timekeeping devices that could measure time to the accuracy of a single minute were a rarity. The stadion was probably derived from the length of racetrack around a typical footrace stadium.
Are you under the impression that god made our measure of time base 12? God didn’t make the hour.
But, I note - in gallons and tenths of a gallon, not gallons and pints.
The newspapers don’t help with the change, as they constantly refer back to old measures. Even now they will quote the Fahrenheit figure in brackets alongside the Celsius. My pet hate is Horsepower, a measurement that seems to be sensible but is clearly not.
I blame the Babylonians. They used a base-60 system, which led to 360 degrees in a circle, 60 minutes in an hour and 60 seconds in a minute.
It’s all their fault. Frikin’ Babylonians.
What natural cycle is the hour based on?
The fact that there aren’t an even number of days in the year isn’t an argument against a decimal system for smaller units. No system would allow an even number of days in the year.
I know. Actually it’s God’s fault, and the Babylonians were stuck with what they had. But hell, neither of them could even invent the steam engine.