People sure like to argue...
Yes, the base choice is sort of arbitrarily chosen. So is the actual magnitude of the units in metric.
But perhaps metric is in base ten because our general numbering system is in base ten? Wouldn't that be weird if someone thought it was a good idea for the unit's base to line up with the number system's base?

Yeah, other bases have an advantage over 10, but no one learns how to use them in general education and every advantage you get from using metric goes away if you use base 12 math.
Go ahead and use an inch or what have you, but for as long as one is working in a base ten number system, using a unit with base 10 divisions is easier. I don't think anyone will tell you that a cm is better than an inch, the magnitude is irrelevant, the problem is that there is no logical conversion up the chain form inch.
No, its not hard to convert 56,789" to miles (even if I new the ratio off hand I doubt I'd ever be able to do that instantly in my head though). But you'd have to be intentionally obtuse to say that was easier than 56,789cm to kilometers.
Obviously normal people very rarely have to use scales as small as nano or micro where metric is far superior (only because the units have names:sneaky

though appropriately enough you usually see imperial done in base ten at that point too with thousandths and millionths of an inch. And in the normal folks life one rarely has to change unit reference frames (i can get away with only using inches and feet, and almost never have to go up to miles in the same conversation). But having a systematic unit base sure is helpful for those of us in the sciences and tech industry!
So clearly the USA should go to an imperic system. 10 inches in a foot, 10foot in a something, 10 something in a something else, 10 something else in a mile. Then they can have a base 10 system and be different!