

Very well said. There is also an effect at play here where the more dire an accusation is, the more our natural tendency is to believe it. Take a more extreme example: pedophile. If your neighbor is accused of being a pedophile, however flimsy the evidence, people are going to start acting as if it is true.
It’s logical behavior, in a way, because dangers with more serious consequences need to be taken more seriously. Its safer to just assume a dangerous threat is really a threat even if you’re not sure about the data. This is terrible for those with suspicion cast on them, but it is a thing.
I’m pretty sure giving the finger is entirely cultural. If you met a human from a group with no contact with the rest of the world, I don’t think the middle finger would mean anything to them, unless they infer something from your attitude and context.