The biggest problem is that what a lot of people know about Kissinger is "folk knowledge" they picked up from other people, and this gets passed down as a game of telephone until it's common knowledge, but no one has bothered to check if it's accurate or not. It doesn't help when there are articles like the Rolling Stones one that's been posted, which seem more interested in cherry-picking facts to fit the narrative then in actually looking at what happened with open eyes.
A few years ago, I thought to myself that since people talk about Kissinger so much, I should go and look at what he actually did. I was surprised to see that he didn't seem to be the driving force behind bad policy decisions in the Nixon White House. He was certainly involved as National Security Advisor, but most of the time it looked like Nixon would have made the same decisions without him. Yet for some reason, Kissinger is usually blamed much more than Nixon.
For instance, at least according to the State Department Historian[1] it was General Creighton Abrams that first suggested bombing enemy bases in Cambodia. Nixon agreed, and involved Kissinger, who was the National Security Advisor. But the bombing is usually presented as Kissinger's bombing of Cambodia. General Abrams isn't mentioned in the Rolling Stones article at all. Compare the Google results for "Creighton Abrams Cambodia" with "Henry Kissinger Cambodia" to see how slanted things are.
That's not even getting into the fact that blaming the Khmer Rouge on the bombing campaign is an extreme stretch. But that's how people approach the folk knowledge - they get told something is true, believe it to be true, then stitch together whatever facts they can find to support the narrative they've already set their mind on.
[1] https://2001-2009.state.gov/r/pa/ho/frus/nixon/vi/64033.htm
The Nobel prize is based on explosives. Most scientists 100 years ago were eugenicists. It's difficult to judge people's beliefs and decisions outside of their era. That doesn't mean that you can't build a moral or ethical system outside of it, but they're all based on assumptions of what is good.
It's not like there weren't people calling out Kissinger contemporaneously, or even Lincoln (for his handling of the Dakota). It's more weird when people obliviously deny recent history or create hagiography upon their death.
But we somehow feel compelled to weigh war crimes that lead to the death and suffering of millions against other positive accomplishments as if one justifies the other. We're basically conceding to Kissinger yet again by evaluating his legacy in terms of realpolitik.
I'm not saying his legacy is positive or negative overall, but folks need to look at both sides of it. He's a great example of someone who had a major hand in a lot of major decisions and has a very very mixed legacy because of it.
Things are much blurrier than we make them out to be these days. Anyone who has a major impact often has significant positive and negative impacts. Kissinger was not a one sided character.
And with that said, I can't believe I just defended Henry Kissinger, but it's still worth saying...