I'm not sure you'll get agreement on how many may have died due to the WTS teachings, and whether it's a net loss of life vs those they help prevent.
But the JWs are not at the same level of "cult" as what most people imagine a cult to be ("heavens gate" type).
Only 909 people died at Jonestown, a third of them children. The Watchtower is an apex predator killing machine compared to them. Think about it:
1. Deaths due to blood ban
2. Deaths and suicides due to drug overdoses to try and deal with the pain of lost family
3. Imprisonments due to loss of trust in authority figures (Satan runs to governments)
4. Deaths and suicides due to depression
5. Deaths and suicides due to alcoholism
6. Deaths due to rejecting National allegiances as appropriately allowed in Christianity.
7. Deaths due to organ transplant ban.
8. Deaths and suicides from the belief that when you die your sins are forgiven.
I watched the testimony of a young woman the other day (pioneer sister) who told the tale of what happened to her when she tried to leave the org. Her parents took her to therapist after therapist trying to figure out what was wrong with her. Finally they took her to a JW Psychiatrist who prescribed her powerful anti-schizophrenia medication.
It totally zonked her out. In one of her drug induced stupors, she asked her dad if he was proud of what he was doing to her. He admitted that it truly bothered him, but he didn't know what else to do. She escaped her home and moved in with a disfellowshipped aunt who was into new age stuff. Her adult son (cousin) then raped her. She would go to work early everyday just so she could have a quiet place to cry. She married the first guy who showed her some sympathy at work. You guessed it... more victimization and abuse in their marriage and eventual divorce, but now with two kids to care for. She eventually trusted in God as a Christian and has since remarried to a wonderful man. Married 6 years now with one child of their own.
I know an unbaptized (and doubting) young man who was encouraged and pressured by his JW father to marry a newly separated (non-baptized JW) 16 year old girl when he was only 17. Her JW parents had previously allowed her to marry a convicted murderer, so that she wouldn't die at Armageddon for having sex outside of marriage. (She had sex with a school coach at 14 and they found out). Instead of seeing this as rape, the parents saw her as a fornicator and allowed her to marry her new boyfriend - an ex-convict biker she met in the neighborhood. She was only 14 when they married. Her new husband had shot his first wife in the face with a shotgun. The JW parents had to give written consent at this age for her to marry.
The young man eventually became a Christian, remarried and successfully raised two more sons who are excellent examples of character and citizenship. Marriage still in tact after 18 years.
Simon, I don't know if you were a born-in JW or not. But, I have noticed that there is usually a big difference in perception between the born-ins and others whose joined later than birth. 3rd and 4th gens have it the worst IMO.