> I guarantee you you would be able to adapt without any problem.
I guess it depends on how you define "problem". It took me years (probably a decade or so) to get good at estimating measurements. I would expect that to relearn how to estimate using metric units would take a decent portion of that (though probably not all). That is a very real cost to me if we were to adopt metric units. Meanwhile, metric also confers no benefit to me (ease of conversion math is irrelevant when I carry a calculator in my pocket, and I've learned the conversions I need in everyday life). So the cost-benefit analysis of switching to metric would be negative for my usage.
But more to the point, it's fucking rude to come in here as you did and call people "uncivilized" for something as petty and meaningless as which units of measurement they use.