It was an irrational fear of communism in both of the cases really that made a bad situation worse. Vietnam's motivations were against the French colonialism and communism were an ally. But they had their stupid 'domino theory' crap despite the fact that even China and Russia could barely get along.

I mean don't get me wrong "communist states" end in totalitarianism but when their fear ends up pushing other countries towards communism instead of away from it there is no way to describe it but irrational.