The biggest reason the United States was criticized for sending military aid to Central America in the 1980s was Central American countries were not allies of the United States.
people felt diplomacy would have worked better than force.
citizens were not grateful for the assistance.
Central American countries were not democratic.

The biggest reasons why the US was criticized for sending military aids to the Central American countries was due to the fact that the countries  were not democratic.

All though most of these countries today have changed and embraced democracy, it was not always so. People had little say in their own lives.

The military was used to suppress the rights of the people. Those who tried to voice out against the governments were made to pay dearly.

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Central American countries were not democratic.

Explanation:

They were not Democratic, with most being dictatorships.