It's not that weird of a position. Penn and Teller did a show on it based on the then believed data that vaccines cause autism. (Which has now long since been discredited.)
They showed the statistics of dying/paralysis/etc were far greater than the chance of autism. So in their opinion, even if vaccines caused autism ( the debunked paper showed a tiny percent chance) , it was still safer to take the vaccine.
Even if it wasn't autism, there is a tiny chance your child can have a dangerous reaction to a vaccine. I was nervous with my children but had it done anyway. My son had a minor reaction to the Polio shot and lost the ability to walk for a couple of days.
It's worse than blackmail because Trump promised nothing in return. Give us money and we will defend Ukraine was reasonable. Zelensky originally agreed when he thought that meant Trump would defend Ukraine.
Instead Trump wants Ukraine to completely surrender and then pay him to surrender.