It's a bit more complicated than that. Imo while America holds the lion's share, both western powers hold blame.
The jeju uprising had a lot less to do with socialism/communism and a lot more to do with Korean independence. After the Soviets and Americans decided to spit the country in half in a shared occupation, there was supposed to be a five year trusteeship until both countries left the peninsula.
Although there was supposed to be a 5 year waiting period the United states wanted to expedite the ending of the trusteeship, which the Soviet state was not in favor of and so they did not come to agreement . After that the US called led a UN resolution for a unified independence election led by the United Nations Temporary Commission on Korea.
The Soviets fearing that they would lose influence in the North rejected the UNTCOK, and so the UNTCOK election only proceeded in the south. The people of Jeju so close to the colonizing force of Japan were more resistant to colonization and were rightly afraid that the UNTCOK would solidify the 38th parallel and rebeled.
In reality both sides could have made compromises throughout the process, but we're both worried about losing influence over a strategic location. Imo it's what happens when western nations believe they have a right to occupy foreign nations.

