Heck, faced with a rapidly spreading virus that can kill in 2 weeks (for the general public at a very low percentage, for our elderly neighbors a lot higher), a large majority of humans turned to angry denials and conspiracy theories to justify to themselves that "it's not that dangerous!".
We are so fucking dead.
When somebody says something isn't that dangerous it always comes with an unstated post-text of 'for an average person of average health.' Each year the flu kills hundreds of thousands of people. As the population ages, and thus has more individuals in senescence where your body is basically just breaking down, that will increase into the millions. But yet it's still not unreasonable to say that the flu isn't that dangerous.
And you might think I'm being disingenuous with these facts and perhaps e.g. all those deaths from the flu are just in Africa or wherever. Whereas in reality it's the exact opposite! Places like the US have a substantially higher than average mortality rate from the flu. Globally deaths are around 700k and in the US it's around 50k. We have 4% of the world's population, but 7% of the world's flu deaths. The reason is because it's not about healthcare, vaccines, or whatever else. It's about the amount of people in senescence.
At a certain age, and the subsequent state of health it entails, lots of things that indeed 'aren't that dangerous' turn into life-ending threats. For some contrast that most aren't aware of, the average age of mortality of the Spanish Flu was 28 - which made it a completely terrifying freak outlier in terms of viruses, which generally affect the very young and very old most severely. Nobody would be saying that the Spanish Flu is not that dangerous in modern times.
Well, maybe search for the keyword "long COVID" and see how it has caused a lot of suffering even among young and otherwise healthy individuals.
Also, people seem to forget that exponentials go up very fast, so an "average person of average health" would be very selfish to not make the necessary precautions to limit the spread of the virus as much as feasible.
You vaccinate yourself to protect yourself. People who are vaccinated for a disease can and do spread said disease. It's this way for literally everything. The claims that you cannot spread COVID if you're vaccinated were simply false. Vaccination can have a mitigating effect of course, but we were never going to be able to eliminate COVID with something like herd immunity.
The only virus completely eliminated by vaccines is small pox, and that was largely because of a number of ideal factors. The top two are probably that that no animals carried smallpox, only humans. And the second is that infection or vaccination provided lifetime immunity of effectively 100%. This dramatically reduced its potential for mutation and meant that getting rid of it in humans would get rid of it - period.
Coronaviruses, by contrast, are transmissible between humans and animals. This means even if you fully eliminated it in humans, it could, and probably would, come back. This is why flus are basically impossible to get rid of. If you believe CDC numbers then US flu deaths in 2020 were essentially 0, yet now it's back like nothing ever happened. Even the Spanish Flu is still with us as a variant of the common flu. But fortunately most viruses trend towards less lethal mutations over time. Probably natural selection in play - killing your host is not a great path to survival and reproduction.
As for long COVID. I'd rather defer that conversation for a few years. Research on exactly what it is and exactly what causes it is ongoing, and so debating it at this point is just going to be speculation.
The reality is that COVID caused lockdowns never had anything to do with the lethality rate. It had everything to do with hospital pressure - there's a limited number of ICU beds and COVID was the annoying combination of spreading easiliy and if it went bad, you'd occupy a bed in the ICU since you needed very active monitoring. If ICU capacity is exceeded, you get into the really ugly business of having to triage who can get necessary first aid. Governments and hospitals both would really do anything else than have to decide whether or not you leave the weak and elderly to die of diseases because you lack the space to handle them. (Not to mention the personnel shortage; a lot of other medical procedures got delayed because of ICU pressure. Even if they did have enough beds, that wouldn't necessarily translate to enough people to care for patients, and you'd end up having to triage non-COVID procedures too.)
That is what caused the lockdowns. It's also why after the first two vaccine waves, the pressure on hospitals was heavily relieved, leading to most countries lifting their lockdowns. Even just being vaccinated once gives you enough immunity against COVID to usually not need a hospital visit. The disadvantages of a lockdown even on just a healthcare level outweigh the benefits when you don't have a dangerous superspreader on your hands.
Mental problems were up massively during the lockdown period since humans are social creatures; physically there also were major spikes in seasonal diseases for the next year since they never stopped evolving, while we stopped getting them, meaning our bodies didn't have the time to adapt to them... So we got all the seasonal diseases thrown at us at once.
Which virus turned "a large majority of humans to angry denials"?