"My dads friend has set up a charity about this.
His ds caught Chciekn Pox and then got Leukemia as a result and died
He is trying to make parents aware that this getting kids together to get chicken pox out of the way is a very bad thing.
He is horrified everytime he hears about it.
So YANBU"
It's truly terrible what happened to your dad's friend's ds - a genuine tragedy, but mercifully a very rare and unusual tragedy.
Many minor illnesses can lead to life threatening complications in a tiny minority of cases - this is not a reason to 'throw the baby out with the bathwater', and it remains a sound principle to contract CP when young (and possibly therefore to willfully expose your children to it)