That the Americans don't like the term witch or witchcraft shows the puritan roots of its own Christianity, which left Britain because they considered the British too liberal in their practice of Christianity. Says loads don't it.

Don't overgeneralize things. Most puritans settled in the northeast coast, of what is the U.S. And they were a very small group compared to the number of colonists that came to the U.S., during that time.

Along with this, most of the other colonists didn't like the puritans at all.

While other groups settled in other parts of the country. Scottish and Irish came over during the seventeen hundreds. Also, during the seventeen hundreds, a lot of Germans also moved to what is now the southeastern U.S.

And there are others also. And while it is not talked about a lot. There are some other religions in the U.S. that are practiced, but in broad daylight, in the public.

For example, the movie, "The Garden of Good and Evil" is correct. Savannah Georgia rivaling New Orleans, in the numbers of those that practice Voodoo.

Now, back to Harry Potter. The wizards in english were very secretive able practicing magic, keeping this secret from the general public.

Also, they censored their news, to the point they were willfully ignorant of the culture and technology of the outside world. I doubt most of them even knew about some of the more destructive weapons made from technology. Such as modern firearms up to nukes.

If the wizards are that ignorant of what is around them, then Wiccans, and other types of magic practitioners, in other parts of the world, probably completely fell under their radar.

One loophole for stories is that if something is not mentions, such as Wiccans, or if the people that talk about something not existing is showing to be ignorant about such subjects, and possibly wrong, than such things can still exist in those stories.