It's really unfortunate that vaccines got sucked into the culture war / tribalism / political divides. That meant that a dialogue about risks and benefits of deploying a response to a public health crisis got tinged with distrust, anger, and division in a way unprecedented in modern times. What I've seen is that it's raised the temperature of every interaction to anticipate the worst possible response and preemptively defend against it. Threatening emails without provocation sound a bit like that dynamic. It sucks for everyone. But it's hard to de-escalate.