We all know that the doctrine and dogma of the WTS is completely false, so I'm not even going to include topics like "trinity" or "gehenna" or anything like that in my personal list.
But I'd like to see what other people list as their top five most harmful JW teachings.
#5. Females in the congregation are inferior to males.
#4. You must override your personal conscience in favour of WTS rules, even when you know it's wrong.
#3. Shunning Disfellowshipped™ and Disassociated™ individuals, without being allowed to form your own opinion or hear their side of the story, even when it is a family member or close friend, this teaching destroys families and results in far too many people taking their own lives from the agony of being rejected by the only people they have ever had relationships with.
#2. Forsaking higher education, well-paid employment and planning for retirement.
#1. The No-Blood rule has cost more lives since it was first introduced by Rutherford than Jonestown, 10 times over.