That's not the issue.
The issue is that the few who do go public need findings to prove their claims. They either cannot find proof, or they make them up. It is just their opinion about vaccines. They have nothing to back it up except conjecture.
Case in point, the 1998 Lancet Paper that implied an Autism link between the measles, mumps, and rubella (MMR) vaccine, you know the one that people still falsely cite to "say" there is a link, was retracted by the author after he it was proven that he was not only incorrect, but he was fraudulent.
Those against vaccines, like the ones you are talking about, have no medical or scientific evidence to support their recommendation. They don't go public because they will be proven as quacks.
If they had true medical or scientific evidence to support their claims, they would not hide in the shadows. They "think" there may be some issues, so they recommend against vaccines, hoping that their patient, your child, does not fall into the "low kill rate."
The odds are that it won't be your child that dies....but what if it is? I am not willing to risk my children's life on a gamble, hoping that my children are not the ones that will die because their immune system cannot beat the disease.
The anti-vaxxers are still as of today trying to find a link between Autism and vaccines to vindicate themselves. They still cannot find one. You know why?