They already do. They refuse blood transfusions when needed, for themselves and for their children. So they don't have mass suicides like Jonestown, Waco, Heaven's Gate or the Solar Temple... but I bet the body count for JWs dying for lack of a blood transfusion is higher than all these "cult-driven mass suicides" combined.
Were it not for the WTS doctrine regarding blood transfusions, nobody in their right mind would refuse a blood transfusion if their life depended on it, and that includes JWs. There's no way the WTS can escape culpability in this matter - they have taught that doctrine for almost 60 years. They declare that a JW who accepts a blood transfusion voluntarily is No Longer One Of Jehovah's Witnesses™. You can't convince me that refusal of blood transfusions isn't an integral part of the JW belief system, that all these people independently and without being influenced, coached or coerced read the bible and decided that the passages they use to justify their dogma meant that they ought not accept blood transfusions.