Gerbil I don't understand your points. I'm not sure whether it's my tiredness today, you not making much sense, or me being a bit dim, but nevermind.
For several reasons using the name Karen as an insult is nasty.
It's extremely sexist and ageist (and in the UK, classist). Whichever country you're in.
But yes it's also racist.
First, because people can't help being born white (or middle class or American) anymore than others can help being born black or brown (or green, if they're Martian). We are all much more than our skin colour, just as we're much more than our eye colour. People are individuals.
Throughout history, the vast majority of people (of all skin colours, including white) had no privilege. That continues today.
In the UK most white people had no voting rights, no say in the country's affairs. Ensuring enough food to survive was their main (often only) concern. Frequently they couldn't even manage this.
This doesn't mean that any form of racism (whoever it's directed at) is ok. Nor should it be ignored, dismissed, or excused. But I don't subscribe to the North Korean notion of guilt by association. It's sinister and divisive.
Separately, it's not ok to use an ethic group's name as an insult. That's not the same as it being someone's given name, which is a compliment and has a long history (unrelated to the Karen people) as a name (I believe it's popular with Hindus as well as Westerners).