Here is my big problem with the use of the 1930s Germany imagery when talking about Muslim terrorists living in Britain: The propaganda of the 1930s was a lie. The lies were spread by the Nazi party to delegitimize and dehumanize the Jews of Germany and Europe. The Jews were scapegoated by a party that found a way to unite Germany on a cause that has ever united the world: Hatred of the Jews.
The Jews of Germany did absolutely nothing of what Hitler accused them. They were not out to destroy Germany.
On the other hand, MI5 has concrete evidence that Muslims in Britain are plotting terrorist attacks. Muslims in Britain—British citizens—have perpetrated terrorist attacks. They have murdered British citizens. They have murdered Israeli citizens. The reason that the MI5 warning that 2,000 Muslims are being watched for terrorist links is not comparable to the lies of the 1930s is because what the MI5 says is true.
The comparison is completely invalid.