Initially, Vietnam did try to purge the pro-West factions which resulted in many people fleeing Vietnam including many Han Chinese. However, being victorious in the Vietnam War has emboldened Vietnamese government. Briefly after the victory, Vietnam decided to unify the Indochina and wage wars with its neighbors to become a regional power. Afterward the honey moon period between China and Vietnam was over and Vietnam decided to ally itself solely with the Soviet. A border and SCS conflict with China and subsequent events ended Vietnam's ambition.
In the late 80s, Vietnam began to realize that the Soviet downfall is imminent. That's why it reached out to China for peace and attempted to copy China's model by opening up its economy. In the 90s, many Vietnamese returned from oversea and pro-West factions in the South is strengthened due to the focus is turning to economy. Vietnam has slowly become pro-West and anti-China become more prominent.
In the 00s, Vietnam needed a distraction for its internal problems as high inflation and the collapse of welfare slowly built resentment among its people. Vietnam decided to incite nationalism and anti-China as a way out. Schools textbook slowly started to eliminate negative American atrocities and depicted the historical grievances with China as the main theme.
Vietnam did tone down a bit after riots against Chinese including Taiwanese factories dampened investment. However, the Vietnamese government has become very corrupt and the thinking of becoming American vassal state to contain China become dominant. At the same time, Vietnamese military slowly and decisively become the king maker as it involved in economy has made it not needing the Vietnamese government anymore. Vietnamese military needs to justify its spending so China became the scapegoat. I don' think there is a way to turn back the clock. Most Vietnamese have been brainwashed to forgive the Americans and hate the Chinese.
It is like many Hong Kongers still dreaming about the UK would come back for them and the US would come to save them from China even though the colonial period in HK is also full of atrocities. The West just knows how to sell its poison pill and brainwash the people to think democracy can resolve everything and the West is their savior.
