Why famous scientists supported Nazi regime? Aren't scientists supposed to be smart?
Also, a lot of people are trivial to manipulate and have emotional weaknesses that are easy to abuse by skilled manipulators, smart or not.
Majorana basically disappeared in 1938. It has been suggested that he could see the feasibility of weapons using fission (Leonardo Sciascia wrote a play about this). Opinions vary and the issue is cloudy and ripe for fiction.
How do I know what I'm doing in life is right? By what mechanism could I ensure that I believe someone who tells me that Jews aren't the cause of all evil if I lived in ~1940 Germany? What makes people increasingly vote for racist parties since covid? The average person hasn't gotten any smarter or dumber in many thousands of years; evolution is not that fast. At best, genes might be expressed differently based on environmental factors, but I'm not aware that this is a factor for the aforementioned inhumane beliefs. How "scientists" (or anyone) could believe this is a really good question, sadly
Of course, this is ignoring the group that did fight against the nazi regime and/or beliefs. This is just about the (sufficiently large) group that could be convinced to work towards inhumane treatment or even genocide
¹ we can all do amazing things when we have the right idea in the right situation with the means to execute it. Of course, good ideas occur to a smarter person more frequently, and they might be inclined to become scientists because it's an environment seemingly meant for working on new ideas, but that doesn't mean everyone there is per se smart. Lots of people are only topically smart (not to be confused with topical knowledge: I scored both top % and bottom % depending on which part of the iq test you looked at, so that's not about knowledge but about abilities. Many people think I'm smart, but I think they mainly notice the parts where I'm unusually good rather than the 'boring' parts where I perform normally or below average, or they attribute it to laziness)
> How do I know what I'm doing in life is right?
I start with humility, as you already have: We don't know if we're doing the right thing. (The great physicist Richard Feynman maybe said it best, "The first principle is that you must not fool yourself - and you are the easiest person to fool.") Notice that those doing bad things these days embrace brazen arrogance and power.
Wise, good people are hesitant to embrace power; not only do we lack the knowledge to know if we're right, power corrupts. The founders of the US purposely diffused power away from one individual; George Washington declined it, repeatedly. In the most popular fiction of the 20th century, the Lord of the Rings, what distinguished the good guys is they destroyed power and feared using it themselves.
That's one reason it's essential to sharpen our critical thinking and judgment, because doing good requires finding the best way forward as frail humans through uncertainty.
(That doesn't mean doing nothing or never using power. We need to use our best judgment.)
> I wonder how large groups (not just a few outliers) can be convinced to believe it.
Humans are group creatures; we and our primate ancestors all live in sizeable groups and not alone (compare bears or sharks, for example). We are programmed to move with the herd.
The herd is guided by social norms. It's naturally very hard to resist them because we fear most being outcast - what feels worse than shame and ridicule? - in part because we cannot survive well or for long alone. You can't get far in life without social connections; it may ruin or even kill you when you need help - and you will - and have nobody to call.
So it's very hard to be the only one at the meeting, when everyone agrees and is moving forward, to raise your hand alone and say 'stop, this is wrong'. For one thing, you may be ineffective and dismissed, lose reputation, and lose group standing. Outcast. In the HN context, this happens to innovators: what is the first response to your innovation? 'First, they laugh at you' - ridicule. Being a true innovator requires violating social norms, which is hard even when it's just technology. Nobody wants to work for years being laughed at by family, friends, and important business contacts (and you never know if you'll be successful after all, for reasons having nothing to do with your innovation).
Sophisticated communicators know this and manipulate groups and the public. Recently the Republican Party in the US as been much more sophisticated at communiation than the Democrats (IMHO), at least in this respect. You see them wield ridicule very effectively, making many left-wing ideas outcast even among centrists and relatively moderate Democrats - as a good example, climate change is factually very well-founded as the moderates and centrists know, but raising the issue is socially outre. Everyone will smirk and walk away from you.
An important part of doing the right thing is having perspective and awareness of norms, and the herd mentality, and to make the right choices regardless while still being effective and not outcast. It's not always easy and takes courage - grace under pressure, not shrillness.