One of my major disillusionments:

A long time ago, a chess-playing buddy introduced me to one of his law professors. We all spent some time talking about this and that, which I remember being very interesting and pleasant. This prof was very renowned/important and, as a lowly university student, I was impressed by how humble he seemed. He somehow made you feel like you were the important one in that room. I saw his behaviour as something admirable and often related that meeting, explaining that this was how a truly worthwhile person behaved.

And then one day I was informed that this man, whom I so admired, had provided the legal arguments used by the Bush administration to justify torture, arguments he had apparently borrowed from a novel to justify the Israeli torture of Palestinians.

It was the 'ticking bomb scenario', a bad-faith argument that posits torture as the effective solution to preventing some horrific and immensely catastrophic event (a nuclear explosion, the end of the world, whatever). It's argued that preventing such an event must surely justify torture. And thus this argument can (and is designed to) justify anything you want ... seriously(!) ... no just the torture of some suspect(s) but even that of their families, children ... basically ANYthing whatsoever (as long as it's not as bad as the major catastrophe itself).

And this childish argument has since been used to make the US join the torture-states, with the side-effect of making the USA also unable to (credibly) criticise other states for torturing people. And as a result, both directly and indirectly, the world became a worse place all around.