I think even if they had all their religious teachings generally right, their organizational claims are still quite presumptous and fantastic.
Terry made a great point. The WTS will imply their teachings are human and fallible ONLY in the context of of thier past failures. Present teachings are promoted as if they were the explicit word of God, not potentially fallible human interpretation. So whether or not the WTS is viewed as imperfect humans or as God's direct representatives totally depends on the context of the discussion.