The United States "knew about and did nothing to stop a series of nerve gas attacks" carried out by Saddam Hussein's Iraq in 1988 as it fought a brutal war against Iran, Foreign Policy reports (emphasis added):
... the United States learned through satellite imagery that Iran was about to gain a major strategic advantage by exploiting a hole in Iraqi defenses. U.S. intelligence officials conveyed the location of the Iranian troops to Iraq, fully aware that Hussein's military would attack with chemical weapons, including sarin, a lethal nerve agent. The intelligence included imagery and maps about Iranian troop movements, as well as the locations of Iranian logistics facilities and details about Iranian air defenses. The Iraqis used mustard gas and sarin prior to four major offensives in early 1988 that relied on U.S. satellite imagery, maps, and other intelligence.
Not that Americans are "terrible people," as one commenter put it, or that President Reagan and the folks in his administration were terrible people. The lesson to be drawn from this historical episode, as from so many others, is that U.S. leaders do in secret things they'd never do openly. With great power and the cloak of secrecy, the temptation to act immorally proves irresistible.
Most people in the Reagan Administration would've been mortified to stand in front of TV cameras and say, "I decided that we should help Saddam Hussein to kill Iranians with chemical weapons." Forced to embrace that approach openly or not at all, policy may have been different.
But the policy never had to be explained to the American people or the world. The American personnel who carried it out never needed to defend their actions to a critical press or the public.* Some people believe America did right back then. The rest of us should reflect on the lessons to take from our wrongs. Taking sides in a war like Iraq versus Iran almost inevitably meant sullying ourselves. Acting in secret all but guaranteed questionable actions would be carried out in our names. And hindsight hasn't been kind to those who claimed our morally dubious acts were necessary. What did the U.S. gain from an Iraqi victory in that war? It's an enormously complicated, ultimately unknowable geopolitical question. But seen in light of the fact that the U.S. went on to spend trillions of dollars and thousands of lives fighting Hussein's Iraq, in part to "rid him of WMDs," it's hard to believe aiding his sarin attacks in 1988 was a necessary evil.
What we must understand as citizens of a superpower, if we're to restrain our excesses even minimally, is that Americans are as capable of acting immorally as anyone else. This country has often been a force for good in the world, but not because our people are more moral than people elsewhere. It's our system of government that's exceptional. The people who designed it understood that power corrupts, and that no one can be trusted to wield it without checks and balances. Representative democracies almost always do a better job than autocracies restraining the worst impulses of the people in charge -- but when American policy is made and carried out in secret, often in ways its own citizens would reject, we start to act more like an autocracy.
And our reputation deservedly suffers when the truth outs, as it always does.
When humans find themselves greatly empowered, and able to act in secret, they often do morally monstrous things, sometimes with the best of intentions. Part of our job as citizens is to never trust our leaders with that sort of unchecked power, for their sake, for ours, and for the sake of the world. That's easy to see when looking back at the bad behavior of leadership a couple decades ago. But those men were no more or less moral than the people leading us today. We'd be a more moral country if we were better able to face our capacity for acting immorally.
*Or their own families, for that matter.