The repressive regimes of the south at least one certainly, were characterized by religious repression. One in fact being of the catholic variety and most noteable and verifiable in history. Not to speak against that religion or any other but all can be misused and were in colonialism and extensions of such. The despotic and repressive south vietnam regimes were backed first by the french then by the US. So this take is not unknown nor indefensible.
People even to this day refuse to admit the domino theory and all that was totally nonsense, even though one of the molders and true believers of that at the time, stated quite clearly in his writings(Robert McNamara) it was a untruth. Vietnam was largly a nationalistic struggle, and not largly a communistic chinese inspired struggle, as their war with China very shortly after the defeat of the US proved.
Even today it is vietnam first communism second or third and religion and buddhism were part of historic vietnam and not part of the colonialism that ruled prior. Japan relatedly as a response to catholicism and its colonial influence at one time virtually outlawed it years ago.
Don't take my word on this stuff...read wikipedia or other source on the history of vietnam, relgions in asia and other specifics related. Religious and other opression certainly existed in the regimes inspired by and protected by the US, and other colonial powers.
Did not anyone in the land of propoganda ever wonder exactly why so many buddhist monks were killing themselves most commonly by fire at one time in vietnam? This one monk was certainly not alone, though most known of.
"This order considers that progress can be achieved more rapidly during a single month of self-transformation through terrifying conditions in rough terrain and in "the abode of harmful forces" than through meditating for a period of three years in towns and monasteries"....Takpo Tashi Namgyal.