"I am 6'1" tall. Those units are useful. 182cm is a vague sort of weird thing."
That is entirely a matter of opinion. To me, the 182cm seems far more understandable. However, I can without thinking know that you are 1.82m and 1820mm tall. However, it takes some time to work out that you are 73 inches tall and 2.028 yards tall. I know that you don't find easy calculations a valid argument, and I'll get to that later.
"£3/9/- divides evenly into twelve months. (5/9)"
I'm sorry, but I don't understand what you're saying here.
"A pint is a useful amount of milk/beer/beans."
A pint is nearly equal to 500ml. Now, you may argue that 500ml is inferior to a pint as it's not its own unit, but where I come from, a half litre is used as if it were a unit. To calculate how many half-litres there are in any number of litres is a simple multiplication of 2. However, to work out how many pints there are in any amount of gallons is a more time consuming multiplication of 8. Not any more difficult, I admit, but still more time consuming.
"A pound is a useful amount of cheese/meat/flour."
My points from the above apply here also. A pound can very easily be replaced by a half-kg.
People advocating for metric do so on the basis of a base-10 number system which itself is dumb because it's not as useful as say a base-12 system which divides evenly more ways."
Although I myself am a big fan of base 12, a base 12 number system will only become as useful as metric if we move to a base 12 system for all our numbers (Brady made a nice video on this https://youtu.be/U6xJfP7-HCc). If we replaced the metric system with a base 12 system without changing our day to day numbers to base 12, the numbers would grow confusing very quickly. For example, with metric currently 100cm equals 1m. However, if metric was base 12, 120cm would equal 1m and 100 cm would equal 0.8m. This seems far more confusing than the current base 10 system.
"So what if metric makes calculations easier. That just proves that people are lazy and don't want to do maths. The people who don't want to do maths, I wouldn't give tuppence ha'penny for."
Having a easier system is superior. It's not about not being able to do maths, it's about not wanting to waste time. What if the imperial system said that a foot was 7.333333 inches. You could use it with a bit of maths, but it'd be very inconvenient. And say you grew up with this system and it's all you ever knew. Would someone who refuses to use this system be considered lazy and unwilling to do some maths? No. They would be considered intelligent for using the more sensible system.
I realize that this is an extreme example, but it's how it seems to people who realize the superiority of the metric system. An easy system makes things quicker and more efficient.
"I love metric - every inch of the way."
Me too my friend, me too.