1 Tim 6:4 in KIT:
"He has been made to smoke, nothing knowing well, but being diseased about seekings and word fights, out of which [things] comes to be envy, strife, blasphemies, suspicions wicked"
In Marshall's Interlinear:
"He has been puffed up, understanding nothing, but being diseased about questionings and battles of words out which comes envy, strife, blasphemies, evil suspicions"
The word in dispute in this context is "noseo" a verb meaning, according to the Complete Word Study Dictionary of the NT [by Spiros Zhodiates]:
"From "nosos" a sickness. To be sick, delirious. It is used metaphorically, meaning to have a sickly longing for something, to pine after, dote on".
The Watchtower rendering of "Mentally diseased" is probably an over translation, made to envision opposers to Watchtower teachings as not just wrong, but also to be wrong due to a mental aberration that refuses to acknowledge the Watchtower leadership as theological supremos in terms of ultimate truth.
Does this word carry a connotation of "mental" ailment in that the person is considered to be clinically insane? Or is it being used purely metaphorically for those who treat the apostle's instructions lightly?
Thayer suggests: "Metaph. of any ailment of the mind, and when used with "peri" [a word meaning "about" as in 1 Tim 6:4 - my own comments] means to be taken with such an interest in a thing as amounts to a disease, to have a morbid fondness for"
In this respect a perfectly good English equivalent for the Greek would be "being obsessed"
Naturally in the hermetically sealed world of exclusive Watchtower values, they have it both ways:
1. When they have an obsession over trivials such as whether Jesus died on a cross or stake, or where a comma should go, or where even the indefinite article is placed, it is theological rectitude.
2. But when opposers rightly excercise the option of presenting an alternative view to Watchtower absolutes, they are seen as being obsessed.
Go figure.