Some of us still seem to not understand the point of pro-side neutrals. They are not meant to represent countries that slightly favored one side or another but never joined the war. They are in place rather for historical reasons to represent countries that were not yet involved in the war by the start date in 1940, but joined later on. For example, Greece would be pro-allied neutral because they joined the war at the end of 1940, after the game starts. Spain, on the other hand, would not be pro-axis neutral because while the government may have favored the Nazis, they at no point had serious plans to enter the war. If the Nazis moved large scale military forces into Spain, Spain would have fought back. Greece on the other hand welcomed British troops into the country to help defend it and would not have fought back against them.
To show an in game example from Pacific, up until turn three, the United States actually functions as a pro-allied neutral power. They are neutral until attacked, but only if attacked by the axis. Because the US is also a power, they have some special rules which apply to them, such as the ability to build and move around units before entering on the side of the allies. However, it would be impossible for them to join the war on the side of the axis, even if they wanted to.
Anyway though, it wouldn’t make sense for Argentina to be pro-Axis because at no point in the war did they welcome Axis forces into the country (at least that I’m aware of).