I don't think it's fair to lable those who partake as mentally unstable. Not all of them. While it's true that I personally believe the GB are unstable, not everyone is.
When privately celebrated the memorial, I did it becuase I believed what the bible said on the matter, rather than WTBTS dogma. I wasn't unstable, I just figured if the bible was true, then I needed to follow what it said concerning that celebration/commemoration. We wouldn't say that ALL members of ALL religions of the world are mentally unstable, just because they follow a particular tradition, would we?? We may suspect some individuals, but a blanket statement may be unfair.
The dogma of JWism creates an unusual problem about who is "worthy" to partake and who is not. It creates a judgmental enviroment that should not exist, and doesn't exist in any other Xian sect that I know of. It's a man made problem that began with human ideas and exists because of the desire to save face while remaining the boss of you.
I'M YOUR BOSS, BEE-OTCH!!!