"If Islam is like the Ku Klux Klan, then it needs to be banned or expelled."
But, we don't ban the KKK, either. You can find little knots of the racist cretins in many place. They march around in their sheets, with police protection.
Did you think the KKK was illegal? It isn't.
The question is not whether there are 1b or 150m practitioners - we do not guage our decision to respond depending on the size of the enemy - we merely guage our 'type' of response.
Ultimately, the only thing that matters is the preservation of the Constitution: Lincoln, Wilson and FDR all faced up to situtations where certain liberties had to be suspended in defense of our country.
When it comes to dealing with Islam, we have already have an established track record in which a conservative SC will reference.