That excuses nothing. Atrocity is atrocity. Wrongness is wrongness. Don't advocate moral relativism.
If a burgler breaks into my house at 2am, one school of morality would argue that my only moral choice is to put do everything possible to avoid killing him, even if that puts me and my family at risk.
I am not enrolled at that school. There are times when survival cancels the finer aspects of moral philosophy
So tell me, what exactly would you have done in Pinochet's place? Allende's marxists were bombing, assaulting and kidnapping to destroy capitalism. The economy was in shatters... hyperinflation and social unrest. Allende was THAT close to taking steps to consolidate power.
And then a lone voice speaks in the midst of all this terror and chaos... "Atrocity is atrocity. Wrongness is wrongness. Don't advocate moral relativism."
You do know this was not a time for reflection and thoughts. Do you seriously believe the plans Allende had for Chile and South America was anything but brutal repression and mass murders to achieve the ideal communist state?
And are you aware that intellectuals who talk like you... were usually the very first people to get executed by the communists?