Often these opposition parties might use theatrics, exaggeration and outlandish claims to attract attention. In some ways, this might reflect the official channels who spray a lot of fear-based propaganda initially. So there might be an overcompensatory reaction to an overcompensatory action. Not trying to excuse blanket anti-vax theories.
Vaccines are of course great inventions, but sometimes the waters get murky with pharmaceutical companies and their ethically poor track records, suddenly making huge profits and frantic politicians calling the shots on public health. Throw free-speech crackdowns in the mix, and now we have a problem worth talking about without emotion.