There are countless other predictions and doctrines which have proven to be false. Hence, we can rightfully say that Watchtower is a false teacher. Since anyone who follows a follows a false teacher is an apostate, then anyone who follows Watchtower's teachings is an apostate. And yes, according to Watchtower, Jehovah's Witnesses are apostates. By logical deduction we can conclude that Jehovah's Witnesses "are mentally diseased" - Straight from the horses mouth.
I agree, but can't help but wonder why still playing by their rules. Why using their language? Why still defining things by their own terms? I wouldn't call them mentally diseased, I'd call them full of --it.