Let them leave - and then bolt the door

What's all the fuss about preventing the likes of Mohammed Emwazi travelling to Syria to join IS? As long as he, and others like him, don't get let back into Britain, why stop them leaving? Calton would rather they left than stayed to wreak havoc in this country and cost the taxpayer millions in surveillance. Their loyalties are clearly not with the UK but elsewhere. Fine. We can't force anyone to be loyal to us, nor should we. Let them leave and then close the door behind them. The realisation that they can't get back into this country once they've gone may make them think twice about pledging their allegiance to a pseudo-state which is the very antithesis of Britain and British values.