That's an easy one. Ever had measles? Ever had mumps? Ever had rubella? What about whooping cough? You've certainly never had smallpox and if you're in the United States, you've definitely never been vaccinated for it. Polio? That's a thing that happened in the '50s, it's gone now. But the Grishams have that weird kid up the street. And you've certainly seen Rain Man.

So "vaccines" provide an abstract benefit while exacting a concrete penalty: for one thing, your baby cries when they get one and it's a preventable injury. They look at you with deep distrust and shattered confidence. Why would you do this to them? For another thing, if you type "vaccine injury" into Google, it autocompletes with "compensation program" and leads you to vaccine court whereby you learn that apparently vaccine injury claims are so common that there's a federal process whereby Congress made vaccine manufacturers 100% free of liability while also issuing large payouts to those who a jury found harmed by vaccination.

Vaccines are victims of their own success. People who will happily get vaccinated for jungle rot so they can have that vacation in Phuket are hesitant to have their kids poked. And the way we handle it in the United States is fucking retarded from every angle: you bring your kid in for a well child visit and they browbeat you about the fact that you're six days behind schedule to give your kid six shots and you are a Horrible Parent. Meanwhile the doctors themselves jet the fuck out of there because they don't want the kids associating them with pain and betrayal; some Nurse Ratched figure who doesn't smile comes in and stabs your kid like they're veal. And should you say "do we have to?" you'll get an eyeroll and an exasperated sigh, not any sort of patience, not any sort of reassurance, because fuck you, moron, they're the doctor and you're just the dumbass that doesn't believe in a "known public good" and clearly 100% the problem here.

Vaccines are a problem in the United States because medicine in the United States assumes the attitude of "fuck you do what we tell you now pay a million times more than makes sense and you think your insurance covers it but fuck you twice you didn't say mother may I that'll be $215 for making your kid scream for half an hour so they won't catch a disease that hasn't been seen in the US since before little Ashley's grandparents were born."

It's fair to say that asking "why should I vaccinate my kid" in the US is treated with all the patience and scientific rigor of "why shouldn't I abort my baby" was treated in Ireland in the '60s. If medicine weren't an infallible, adversarial monolith in the US, nobody would fight vaccines.