However, there's a nasty subset of pedantry which basically consists of pattern-matching words without truly grasping the meaning and using that as a launching point for a "you're wrong" reply. This kind of pedantry derails conversations and wrecks communities.
That's the kind of pedantry I got above with this nonsense reply about how "in metric they would use liters". As if I didn't know that! A moment's thought would indicate, hey, maybe this guy is not a complete idiot who doesn't know anything about metric, and he probably already knows that neither ounces nor gallons are metric, so let's figure out what he actually meant instead of doing a mindless pattern-matching "you're wrong" reply. That is hostility too. Especially when you keep on going even after the guy explains it.
And of course I get the usual internet double standard, where it's perfectly OK to to write a really bad comment as long as you don't outright use upsetting words, but calling that behavior out is criticized.
I don't subscribe to this idea that "civil" is equivalent to "use nice words". To me, "civil" is about how you behave. If you curse but treat other people with respect, that's civil. If you use nothing but benign words arranged in a way that treats other people without respect, that's "not civil".
If we say that a problem is caused by half-assed adoption of X, it implies the problem can be solved in two ways: (1) Properly adopting X, or (2) Reverting back to no adoption at all. The example you gave can only be solved by 1, because it is an inherent problem of the imperial system. If you take metric out of the equasion, the situation is not affected. While you may have meant to say "the imperial system has problems, let's use metric", one can also understand it as "the transition to metric is causing problems, let's stop it".
For example, "I hate how they're serving a 50/50 mixture of coffee and urine, makes the coffee taste like urine." This does not imply that the problem can be solved by eliminating the coffee.