risking their own health so that the human genome can keep
  battling with and evolving natural defenses against disease?

Diseases evolve orders of magnitude faster than humans. Giving ourselves a chance to evolve also gives the disease a chance to respond and they will always find ways around our defenses faster than we find defenses. Remember, the usual result of failing to complete a course of antibiotics is a new strain of antibiotic-resistant bacteria. Leaving a reservoir of a disease that we have a vaccine for is far, far more likely to result in a new strain of that disease that can bypass the vaccine.

Additionally... what's the point? Any disease that has a voluntarily unvaccinated population also necessarily has an effective vaccine. The development of a effective vaccine equally necessarily indicates that developing vaccines is easier, faster, and better than attempting to evolve defenses. Why try to go back to evolution at all? The existing vaccine works. If it stops working, make a new one. No need for these ad-hoc primitivist schemes.

Society generally takes a dim view toward people who endanger others through ignorant recklessness.

Because they aren’t the canaries at all. Instead they volunteer their kids (and the kids who interact with their kids) as the canaries.

Furthermore, they risk infecting others who, through no fault of their own, rely on herd immunity. Such as those who due to allergies cannot take a certain vaccination, or who did take it but it was ineffective. Herd immunity protects more than just the ignorant.

Young child affected by leuchemia can't go to school nowadays in Italy, because they risk being infected by anti-vaxxers'child and risk their life

People are angry at them because the herd-immunity they are compromising is the only thing keeping certain members of our population alive and healthy. There are some people who, for various reasons, CANNOT receive vaccinations. Not WILL not, or DO not, but CANNOT. When herd-immunity is compromised it's not just the anti-vaxxers children's lives that are at risk, it's everyone who doesn't GET the choice to vaccinate or not that are more vulnerable to disease since it can now spread through the population more easily.

It’s not just that. Some vaccines are less than 100% effective. When everyone is vaccinated, the disease generally doesn’t spread. When enough people aren’t vaccinated, the disease can spread to some fraction of vaccinated people as well.

Vaccinations are not always effective, nor are they permanent. They are a statistical firebreak against an epidemic. Think of vaccinations like transistors. They are modelled as 1 (vaccinated, won't get sick) or 0 (unvaccinated), but that's not the reality. The reality is very few people have an immunity level of 1.0 (won't get sick) on that scale even after vaccination, and some of those who do seem completely immune are that way because their immune system is particularly good at making a particular disease asymptomatic, not (necessarily) because they were vaccinated.

You can still get infected even if you were vaccinated recently. Many vaccinations lose effectiveness after a decade or two at most. Most adults (who are less affluent/wealthy or who don't travel) don't get re-vaccinated for most things because they're at lower risk. The highest risk is in places like preschool, daycare, grade school and college with lots of people in close proximity, and some poor hygiene mixed in.

And hospitals and doctors offices.

Anti-vaxx parents put everyone else at disproportional risk, because children are a prime infection distribution hub for all kinds of contagious diseases.

Because they are not just risking their own health.

I am not a doctor, but my understanding is there is a small bug significant number of people who cannot get certain vaccines due to e.g. immune system issues. "Herd Immunity" through a highly-immunized population generally protects these people because there are fewer reservoirs for a given disease.

Edit: The reason people are mad at anti-vaxxers: their foolishness directly impacts the welfare of some already unfortunate folks.

Am a PhD, and you are correct. These people are however in the minority, and its important to ensure that people don't use this fact as false justification for not getting vaccinated.

They don't just endanger their own health, they endanger us all. Some people can be carriers but not be symptomatic for a pathogen, so they can be walking around spreading a disease like measles but not even know it. With high herd immunity this is not much of a problem because almost all of the people with whom they come into contact will be vaccinated and not catch the disease before the carrier's body eventually fights it off, but with low herd immunity they become a major problem.

If humanity has not evolved a natural defense to these diseases after thousands of years it is not going to happen by some anti-vaxer volunteering to be an evolutionary petri dish. Actually, now that I think of it, humanity has already evolved a defense against these diseases -- by evolving a big brain it figured out how to develop vaccines...

Anti-vaxxers threaten the lives of not only their own children but the lives of others. There are people that legitimately cannot be vaccinated due to deadly allergies or reactions and the selfish behavior of parents who refuse to vaccinate their children puts them at severe risk. Herd immunity is important to protect people that have no other option and when people compromise it for the sake of perpetuated lies it results in disaster.

My mom is currently going through chemo for cancer. Her immune system is essentially zero despite being fully vaccinated.

You bet I get angry: anti-vaxx people are trying to kill my mom and there is nothing I can do about it.

They're not trying to kill your mom. That may be the effect, but it's not the intent. They're trying to have their kids not be autistic. (You can claim that the evidence doesn't support that as a possibility. But it's still what their intent is.)

That's like saying "I'm trying to make it dark by turning on the lights." You can;'t make excuses for them by saying that, even though they are recklessly endangering other lives, they're doing it under pretenses that are false, so it's ok.

I mean, people who attempt to pray away disease instead of seeking proper care has potentially good intent. But that doesn't make them any less negligent when their child dies as a result.

There’s a research paper out there where people who were prayed for had worse clinical outcomes then the control group.

Someone shooting a gun randomly in the middle of a busy shopping mall might honestly claim they just wanted to hear a loud bang - yet there is no reasonable way to say their actions won't kill someone. Therefore they are trying to kill someone despite their stated intention.

What about vaccines for nuisance illnesses where the vaccines have potentially severe consequences? For example, the rotavirus vaccine has been known to cause intussusception in some small but non-negligible fraction of recipients. This is sometimes fatal, and generally involves surgery. Rotavirus typically causes diarrhea, which can be dangerous, but generally isn’t if monitored closely.

Do you call CPS on parents that refuse that one?

“The only vaccine that is missing from many state mandates is the rotavirus vaccine.”

- Vaxopedia.org

Anecdotally, when we were vaccinating our kids, rotavirus was presented as optional or not crucial. I don’t remember the precise wording the doctor used, but I recall it was the one we skipped. A big factor in that was our kids were not in any kind of daycare.

> Failure to vaccinate should result in intervention by CPS and the parents placed on a watch list.

Failure to vaccinate is a big issue, but I'd rather have anti-vaxxers than government taking kids away from parents because the parents refused a medical intervention.

I would rather the government step in than allowing anti-vaxers to keep polio, measles and whooping cough around.

Frankly the government steps in on a lot of things, like when a parent is caught driving drunk with their kids in the back of the car.

What about daily beatings? Anti-Vaxxers put not only their children but many people in the general population at serious of death and should be sent to prison.

We don’t let people drive drunk for good reason, vacations are far more critical.