Note that the election was far from being "the majority of electors" and heavily disputed at the time:

https://en.wikipedia.org/wiki/Salvador_Allende#1970_election

Let's not pretend Allende represented the population of Chile at large, please.

Hoover report on before and after Allende: https://www.hoover.org/research/what-pinochet-did-chile

> In 1970, Allende won 36.2 percent of the popular vote, less than the 38.6 percent he had taken in 1964 and only 1.3 percent more than the runner-up. According to the constitution, the legislature could have given the presidency to either of the top two candidates. It chose Allende only after he pledged explicitly to abide by the constitution. “A few months later,” Whelan reports, “Allende told fellow leftist Regis Debray that he never actually intended to abide by those commitments but signed just to finally become president.” In legislative and other elections over the next three years, Allende and his Popular Unity (UP) coalition, dominated by the Communist and Socialist parties, never won a majority, much less a mandate, in any election. Still Allende tried to “transition” (his term) Chile into a Marxist-Leninist economic, social, and political system.

and

> Many on the left had long believed that capitalism and democracy were incompatible. In a brazen demonstration of its contempt for majority wishes, and for the institutions of what it called “bourgeois democracy,” the pro-Allende newspaper Puro Chile reported the results of the March 1973 legislative elections with this headline: “The People, 43%. The Mummies, 55%.” This attitude and the actions that followed from it galvanized the center-left and right, whose candidates had received almost two-thirds of the votes in the 1970 election, against Allende. On August 22, 1973, the Chamber of Deputies, whose members had been elected just five months earlier, voted 81–47 that Allende’s regime had systematically “destroyed essential elements of institutionality and of the state of law.” (The Supreme Court had earlier condemned the Allende government’s repeated violations of court orders and judicial procedures.) Less than three weeks later, the military, led by newly appointed army commander in chief Pinochet, overthrew the government. The coup was supported by Allende’s presidential predecessor, Eduardo Frei Montalva; by Patricio Aylwin, the first democratically elected president after democracy was restored in 1990; and by an overwhelming majority of the Chilean people. Cuba and the United States were actively involved on opposite sides, but the main players were always Chilean.