When dealing with those pushing pseudoscience, like the antivaccination cult, the most frustrating thing is that they tend to ignore and deny the most basic tenets of science. If denying the fact of gravity would further their goals of “proving” vaccines are neither effective nor safe, they would do so. For all I know, they have.
Water is two parts hydrogen and one part oxygen. What if someone says, “Well, that’s not how I choose to think about water.”? All we can do is appeal to scientific values. And if he doesn’t share those values, the conversation is over. If someone doesn’t value evidence, what evidence are you going to provide to prove they should value it? If someone doesn’t value logic, what logical argument could you provide to show the importance of logic?
If the antivaccination movement didn’t lead to epidemics of long-gone diseases, which can harm and kill children, the conversation would be over. I would just put the vaccine deniers in the same group as evolution deniers (creationists) or gravity deniers (there has to be some, somewhere). I would mock their pseudoscience, and move on. Of course, their denialism does lead to deaths of children, so we have to do what is right, and stop their lies, misinformation and ignorance in every forum we can.
We have to appeal to scientific values, and despite the fact that antivaccination pushers don’t share those values, we must continue to try. I have gotten enough emails and comments from people that they have started to vaccinate because of what I have written, so maybe some child’s life is better because all of us who support vaccines are heard.