Plenty of people have been outspoken against anti-vaccination far longer than it's been relevant today. The introduction of vaccines for the first time was revolutionary in itself; do you think everyone jumped on board with the idea of injected dead/weak cells of dangerous diseases into their body?
Sorry, but seems like children are always the reason to do things. So who gets to determine what is banned and what is not? Who gets to determine what is sold and what is not? What if fifty years from now someone publishes a book about racism against whites and it's banned for seeming like "white nationalism" because of previous censorship? Who gets to decide what is right and wrong? The anti-vaccination papers have forced the scientific community to retort with evidence based trials that strengthened the resolve for it. Yes, a lot of stupid people are going to make stupid decisions. It's just how it is... but if we get every company to do get rid of anything that could potentially hurt, insult, offend, or any variation on a whim because... "oh the children"... then you'll have no control.
Sorry, but plenty of other things could have been censored. Plenty of crazy people published books and stories about the government watching them for us only to realize decades later that they were in fact being observed. What if white people fifty years ago had decided that books about black struggle were propaganda to inspire people to riot against white people? Where would be today if people weren't publishing things that were otherwise not known as true, untrue, or unheard opinions?
Sure, Amazon has the full right and really no ethical consequences to not selling things it doesn't like or agree with. I argue the opposite; Amazon isn't ethically doing anything wrong by pedaling such dumb literature to gullible people. It's capitalism. Whether or not people do stuff about it really seems arbitrary; if they were dumb enough to deny the holocaust then it was only going to be the next big conspiracy for them to believe in anyway.