How far should a tolerant society tolerate intolerance? It’s a difficult question, with no clear answers.

It's a question this country faced in the 1940s, when agents of Soviet totalitarianism infiltrated high positions in the U.S. government and in major labor unions. On the whole, Americans handled this reasonably well, not going so far as Sen. Hubert Humphrey's proposal to explicitly outlaw the Communist party, but removing Communists from leadership positions in the labor movement, the Democratic party and the federal government.

This was, by the way, largely the work of anti-Communist liberals like Humphrey, UAW President Walter Reuther, Eleanor Roosevelt, historian Arthur Schlesinger, Jr. and President Harry Truman.

In this century the threat is Islamist terrorists. How far do we tolerate intolerance? Not so far as to allow terrorists to indoctrinate their children, argues the twice-elected London Mayor Boris Johnson today in a Telegraph opinion article. He writes:

The law should obviously treat radicalisation as a form of child abuse. It is the strong view of many of those involved in counter-terrorism that there should be a clearer legal position, so that those children who are being turned into potential killers or suicide bombers can be removed into care – for their own safety and for the safety of the public.

“Removed from care” is British English for taking them out of their homes and putting them in public institutions or foster care. It’s a striking proposal, one which I’m inclined to agree with, but wish to ponder further.

Johnson is the most colorful figure on the British political scene; I can think of no equivalent in American political life. As a Conservative twice elected from Labour-leaning London, he has been mentioned more than a few times as a possible future Conservative party prime minister.