These schools aren't state-funded, though, are they? And they're not 'day' schools, either. I thought they were evening and weekend schools, a bit like the way we sent our kids to bible class and bar mitsvah coaching.
I don't like what they're teaching, but as long as the kids they teach don't actually carry out what they're taught and don't break the law, as far as I know there's nothing to stop people teaching them.
You can legally teach someone how to tie a noose. It doesn't become illegal until it's actually used as such.