Haha I don't think it's about fear. It's probably about having hundreds of years of using those measurements, and it being very baked in to the language used between people to communicate.
Nobody wants to have to translate between kg and stone all the time. It's tedious. If you live in a country where all your interactions are going to be in one measurement then you're probably just going to go along with everyone else.
Even down to 'goin down the pub for a pint' being a commonly used phrase which doesn't have the same ring when it's ''goin down the pub for a half litre'.
That's the thing, they do use kg. So it is not something they don't know about. Just that stone for people's weight specifically somehow is still in use.
For the pint, I do not think it is about the volume when someone says that. As of they are only going to drink one anyway?! Replace it with beer and it is a perfectly normal thing to say.
Yes. The Brits still use a few non-metric measurements at times. In fact, it was America’s British heritage that got us Americans into the bad habit of using imperial over metric in the first place.
Stone only makes sense for people used to pounds, shillings and pence. For instance, "This costs 3 pound, 4 shilling and 8", and, "I weight 12 stone, 6 pounds and 3 ounces".