"how do you know an ideological extremist when we see one"

Well it's pretty simple really. You listen to their ideas, ideals, values and the language and tone of voice they use. Then you compare it to what known extremists have said. And, if you have a mind, you read the likes of A C Grayling, Tzvetan Todorov, Vasily Grossman and others who were the victims of ideological extremism. Then you make your own mind up. This is what personal liberty is all about. This is what the extremists you support seek to supress.