I don’t believe there are any people who believe that NOT beating their children is dangerous. If you put yourself in these parents’ shoes, they basically see this stuff as poison. What you’re asking them to do (in their mind) is inject their children with poison and for no other reason than because the government says so. It’s just a losing battle, you need to educate these people and show them that they are safe, address their concerns directly.
I would not inject my children with mercury if the government told me to. I would need to be convinced that mercury is safe and beneficial before I allowed my kid to be injected with it. I don’t feel like equating this to physical violence is helpful at all because in this case these parents believe they are preventing harm to their children.