What's the main reason people believe that vaccinations cause more harm than good?

Because human beings are hard-wired to be unreasonable. We’re not naturally good at risk-benefit analysis, we are prone to bias, and our emotions play a large role in our decision making. We are wired to see patterns even if there aren’t any and we tend to believe only information that confirms our bias and ignore or disregard data that doesn’t. Plus an individuals’ lack of knowledge about a particular subject leads them to inaccurately gauge their expertise on that subject (aka they are Ignorance of their own ignorance).

So from the very first vaccine there have been people against them. The “anti-vax” is nothing new. Some people have always believed in conspiracy theories. Some people have fears and search for a reason for their feelings and choose to blame vaccines. A lack of real understanding of medicine and diseases lead people to believe they know more then experts.

So the main reason is that people refuse to acknowledge their own limitations in reasoning.

some idiot reckoned they cause autism and put it online. so people seem to believe whatever is online. it was disproved but too late.

Because not all vaccines are safe. Over 4 billion dollars has been given to victims by the National Vaccine Injury Compensation Program. Vaccines like everything else in life are not all good nor all bad. Some vaccines have helped, but improvements in sanitation and access to clean water and nutritious food were much bigger factors in improving life expectancy.

Many diseases were already in decline before vaccines were made mandatory, and in some cases even unnecessary as diseases like chicken pox can actually help a person!

https://www.bcm.edu/news/cancer/chicken-pox-may-reduce-risk-of-brain-cancer

It started when a doctor wrote a fake report based on shonky research.
He was later stripped of his licence to practice medicine and countless scientific research programs trying to replicate his results have shown them to be completely inaccurate but still the false conclusion he came to is used to stop vaccinations.

the main reason is some nut job "doctor" started it and then later recanted but of course no one noticed the recant.

Somebody made a connection that was really just a coincidence.

vaccines is a wa$$street business
Ben Fuchs on vaccines

There was a rumor going around that some vaccines cause autism, which has been disproven.

Well you all can believe that this is just people being misinformed but the reality is that what was the incident of autism in the 1970 s 1 - in 10,000 children now it is 1 in 36. Do your own research. Wakefield was not disapproved. He is still working and fighting for children, when people like your selves need to wake up and see the reality. We are the sickest country in the nation. Look at the truth. Congress has been sitting on the fraud at the cdc since 2013 and have done nothing why? look at who gives money to our government officials. God it is sad to read these posts. did you check the difference between injecting mercury and swallowing mercury? The mercury injected goes straight to the brain. I had three children vaccinated at the hight of the fraud and each one of my children were damaged. Can any of you see walking down the street parents with children who are disabled.
Every where I go children screaming. get educated look at the science. listen to the liars

Because knowitall stayathome moms want to feel smarter than scientists and doctors. They'll create an epidemic of diseases that were previously eradicated in the industrial world.

That poster is rude, vulgar and ignorant.

It started with people finding out exactly what was in vaccinations, and not understanding what and why.

If I told you I was going to inject you with mercury, you'd freak out. Mercury is toxic! I know this, you know this.
In micro amounts though, it can act as a catalyst for injections - the amount is so small, you probably inhale more via walking around a city, than you do with an injection.
Mercury has since been removed from the vaccinations, but the fear of it is still there, and so the story grows.

Fake internet articles that have either made up or no reliable sources. Jenny McKarthy really doesn't help the cause either.

There's probably no one 'main' reason, but a major cause would be Andrew Wakefield who wrote a fraudulent research paper claiming a link between the measles, mumps and rubella (MMR) vaccine and autism and bowel disease. He has since been struck off the UK medical register for unethical behaviour, misconduct and dishonesty. Unfortunately however, the harm was already done.

See: https://en.wikipedia.org/wiki/Andrew_Wakefield

Because many people are stupid and gullible and believe things they read on Facebook.

It all started when the first MMR vaccinations started, because when the US government chose the best one, there was a rival brand.
The rival brand started the smear campaign againt their competitor. And it became a smear on all vaccinations.

Because they do