I would argue that the piece contains several important distortions, aside from trying to lump together a region from Colombia down to the Southern Cone.
The historical truth silenced by “memory” is that the cold war in Latin America was fought by two equally authoritarian sides.
But it was not. To take the example of Argentina, yes, there were Montoneros and there were incidences of left-wing violence before the 1976 coup. But to suggest that the small leftist group, which was largely destroyed before the military took power, was in any way equivalent to the forces of the State is very far off the mark.
The Economist points out that some human rights groups in Argentina tend to use the figure of 30,000 disappeared and it contrasts this with the nearly 9,000 victims recorded by the CONADEP commission. It is inaccurate and unfair to use the CONADEP list to undermine estimates of the disappeared, and I explained why in detail years ago. See also here for more on the numbers.
None of this mitigates the inexcusable barbarity of Pinochet or of the Argentine junta.
The problem is that it does. You can't equate State terrorists with their victims, suggest that calculations of the disappeared are deliberately inflated, and then claim that you're not weakening the accounts of the dictatorships' crimes.
Memorials are a shorthand, yes. You can't include the whole complexities of a country's experiences on a plaque. Memory, in its wider sense, tends to include the testimonies of victims and relatives and it encompasses a whole range of commemorative acts, both formal and informal. Pulling out the memory/history dichotomy and reiterating the dos demonios theory ("each side was as bad as the other") is a means of obscuring human rights abuses and seeking to paper over the crimes of the past.