What seems to me foolish in standard vaccine refusal is roughly the same as what seems foolish to me in opposition to using the insecticide DEET in areas where mosquitoes carry malaria, which kills many people. It’s true that the DEET causes some significant problems, but it is unlikely that those problems are worse than the many deaths that would result without it. This seems clear just based on historical use of the chemical. Similarly, vaccines may cause some problems but the (recent) historical use suggests pretty clearly that they save lives.
Of course, there are always mistakes. Science is constantly evolving—it is more of a process, after all, than a single state of knowledge. Scientists make mistakes. Worse, sometimes scientists bend to their desires and sometimes industries have enough financial power to change the way science is presented. (Looking at you, sugar Industry!) Given that and a personal distrust of government, I certainly understand when people want to wait for evidence to settle.
A drug or other scientific advancement used too early may well turn out to be more problematic than its worth. But aspirin has been well tested. And vaccines have been well tested. Even the recent Covid vaccines have been well tested. The fact is you are far more likely to die from Covid if you are unvaccinated than if you are. Granted, the odds of dying either way are thankfully slim for most of us. But what people are now faced with is a free and easy way to avoid (a small chance of) death. Admittedly, it’s possible that in 20 years we’ll learn that these new vaccines cause cancer or such. But scientific advancement will continue and the fight against cancer is already far better than it was any time in the past. So the option is between a free and easy way to avoid a chance of death or serious illness now combined with some chance of added problem later that we may know how to deal with and, well, not avoiding that. Maybe this is a judgement call, but the former seems pretty clearly the better option in standard cases. (Other downsides, so far as I can tell, are mostly fictitious. If you’re worried about a computer chip embedded in the vaccine, for example, realize you could have had one put in you when you were born.)