I don't get how any of this was a shock. A lot of vaccines are mandated when you're in the public school system. Most people in the US have gotten these "mandated" shots without much complaint in the past. So much of this seems like rationalization of a purely reflexive reaction to the idea that there's any kind of social responsibility.
Consider the similar backlash to mask mandates. I didn't like wearing a mask, but it's not a huge imposition. Some people treated it like it was greatest injustice they'd ever experienced though. And then they went on to rationalize this emotional reaction by making up shit about masks cutting off their oxygen supply or causing brain damage, etc. All this despite the fact that wearing a mask (or even a respirator) is necessary for a big chunk of the day in many jobs ranging from construction workers to surgeons.