"Suppose that a doctor told you to avoid contact with someone who is infected with a contagious, deadly disease. You would know what the doctor means, and you would strictly heed his warning. Well, apostates are “mentally diseased,” and they seek to infect others with their disloyal teachings." The Watchtower. July 15, 2011; Page 17:
In the U.K. this might be grounds for a group libel action;
Libel is the publication of a statement which exposes a person to:
Hatred, ridicule or contempt or which causes him to be shunned or avoided or which has a tendency to injure him in his office, trade or profession in the estimation of right-thinking members of society generally. Libel is all about words that damage a person's reputation in the eyes of reasonable people.
The first question when you consider a libel action: "Is what I have written basically true"?
If it is not true in substance and in fact then you will be deprived of the two classic defences:
* Justification - you are justified in damaging a reputation because what you are saying is true.
* Fair Comment - the comment complained of has to be based firmly on fact.
Source and further reading.