I have never, in around four decades of living, had an actual need to determine the mass of a given volume of water, or the volume of a given mass of water.
When cooking, I routinely need to split some quantity of an ingredient into thirds or quarters.
Yet I am also constantly told that I'm ignorant and backwards and irrational for preferring a system that optimizes for the latter, rather than for the former. Base 12 is genuinely better for many real-world applications than base 10, those applications are more common in the lives of non-scientists than the applications metric is optimized for, and I doubt you're going to be able to produce a rational argument otherwise.
I remember when some guys thought about building a pool on the balcony, calculating how much water weighs is admitably not ver often used, but when it is the consistency of the metric system is nice.
I work with wood in mm for years and never had any problem with the metric system. Finding the third, fifth or sixth or whatnot is not hard if you are used to it at all. Converting from mm to meters isn’t hard, etc.
Having a number like 666.66 mm probably sounds scary to measure (beyond the religious connotations), but in fact it is a point on a line that is easy enough to find.
Why?
“Global standard” isn’t necessarily an argument for “good.” Why aren’t imperial units the standard? Who actually decided that metric was the right answer?
And as a previous poster mentioned; why don’t we say a megameter or gigameter when talking about long distances? Because ultimately measurement units are really about human understanding, despite ostensibly being “scientific.” A foot as just as scientific as a meter. NASA went to the moon with imperial units and it worked out just fine. People and countries are entitled to their preferences. We don’t advocate English or Chinese to be the global standard language. Or that all countries use euros or dollars. Weights and measures can be perfectly accurate regardless of the units used; the idea that we should either create or adhere to a global standard is not unlike suggesting everyone speak the same language.
Using a country that excels in being contrary, to the point of being the national pastime, is a poor example.
Even then we literally use metric for everything else. And although it is referred to as a pint, it is measured in metric.
Weighing yourself in kilos is a more modern thing, but that is really the only thing.
Standards make it easy for people to work with each other across borders, and most of the world uses metric already. NASA has since then started all of their new projects on Metric too.
I do agree with your point about the fact that weights and measures can be accurate regardless of the units used, the argument against Imperial isn't about accuracy, it's about ease of conversion and changing bases of the unit scale. (Like 12 inches to a foot, but 3 feet to a yard etc)
People who wanted actual definition of units.
Once upon a time if you wanted to sell stuff in my home City you would need to use the city measurements made via a really big stone tablet in the old roman center with various units of lengths.
This was hard to communicate and stuff.
The French decided that one unit of measurement was better than many and made one "easy" (possible) to replicate and validate when the imperial one still used medium sized wheat seeds as measure of pressure.
But now everything is ultimately standardized on the metric system (even the US).
So one need to ask better at what? Better to standardize? Metric no doubt. Better to use? Well this appears to be controversial
Plenty of people are "bilingual" with metric and local. Canadians are universally bilingual with metric and imperial. It's not that hard.