I would argue that it's the last 50 years of neo-liberal economics, often enforced at gunpoint, that has destroyed Argentina.
Strange world you live in as Argentina could only be described as following neo-liberal economics for about a 15 year period from 1989-2003. None of which was at gunpoint.
While the Kirchners aren't exactly paragons of virtue, and their ideological ancestor Juan Peron was worryingly authoritarian, populism and corporatist economics did a lot of good for Argentina in the 30s and 40s.
More strange assertions that confuse the issue. The 1930s and 1940s economy had nothing to do with Peronism since Peron wasn't elected president until after WWII. The Argentine economy in the 30s and 40s were more or less run on normal liberal lines (including some social welfare) with some exceptions.
If the United States had treated developmentalism and nationalistic populism as a potential ally as opposed to just another example of the Red Threat, Argentina might be highly developed. The industrial base created by the tariff walls most likely could have been heavily reduced over time by Western pressure, forcing Argentinean firms to make themselves more efficient slowly. As well, without American backing, Argentina would never have had such a long period of military rule. That would have strengthened its democratic institutions, making it a better place to do business and less corrupt.
I think this is completely false. The March 1976 was done more or less completely internal to Argentina. US involvement was mainly that it knew about the coup ahead of time, did nothing to stop it, and let the plotters know they would not be punished for it. While terrible behavior, it's not like the US initiated, planned, or actively supported it. Would it have happened without US letting the plotters know there'd be no negative consequences? Hard to tell. Latin America had a long tradition of dictatorial rule, and Argentina was really falling apart internally at the time. I think it would have happened even if the US was caught be surprise vy it. Argentina's generals have never needed outside prompting to take over the government.
In any case, military rule lasted only from 1976-1983, and their economic policies cannot be said to be neo-liberal at all. The junta was divided in terms of what to do. While some favored what would become neo-liberal policies, others were not - supporting the old Peronist line, and the general economic policy was a confused mess. I see it more in line with the previous Peronist policy than against it. So this 8 year period - the closest I can come to an "enforced at gun point" scenario - certainly does not fit your description of 50 years of neo-liberalism.
The time period where Argentine's economy declined from being one of the wealthiest in the world to an underperforming basket case is precisely when the Peronist economic policies you like determined economic policy.
Most of Argentina's economic problems can be tied to Peronism. He destroyed Argentina's export economy in order to suck out as much money as possible to provide for an overly generous social welfare state that Argentina was not able to afford. His nationalizations did nothing to improve the economy. His policy of import substitution was the wrong one to take in the post World War period. It made Argentine businesses uncompetitive internationally, increased costs domestically, and created large structural problems. By enshrining government intervention in the economy, he encouraged corruption and degraded the rule of law.
The big failure of Argentina's neo-liberalism experiment was keeping the perso pegged to the dollar too long. Originally done as a sign to prevent future inflation, it had become an economic fetish that didn't reflect the actual comparison to the Argentinean and American economies. If they had allowed a normal exchange rate, they probably could have weathered just fine and continued to grow. They didn't which created the huge problems for Argentina in 2001-2003. Of course, fixed exchange rates is probably the major exception to neo-liberal economics the Argentine economy had during its neoliberal period.
Both Kirchners' economic policy provided for short term economic improvement over long term fundamentals. This can be justified in the short run in order to avoid social instability. But it was just a short term, slap-on-some-duct-tape fix. In order to keep it up, the Kirchners have made increasingly unwise mistakes. Many economists now expect the economy to blow up AGAIN in the next few years as Cristina Kirchner makes even more desperate policy decisions to keep the scam afloat.
In order to see the magnitude of Argentina's problem, we can compare it to Chile (whose policies are undoubtedly neoliberal) from 1998 to 2010. Between 1998 and 2010 Argentina's GDP (as measured in dollars) increased by 24%, while Chile's increased by 156%. Despite having only 38% of Argentina's population, Chile now has 55% of Argentina's GDP. In 1998, Chile's economy was only about 25% of Argentina's. How long before Chile surpasses Argentina in terms of its economy? It might happen in 10-20 years. If the Kirchners' policies were really working, this wouldn't be the case.
Argentina's main problem is its history of caudilloism which has nothing to do with US foreign policy or neo-liberal economics.