It's not so simple, the rampant corruption under Ngô Đình Diệm, misappropriation of aid, etc. shouldn't just be swept under the rug. Hindsight says remaining capitalist probably would have been better for the average person, but it wasn't so obvious at the time.

Johnson was a warmonger, exaggerating (or possibly faking) the Gulf of Tonkin engagements to justify full escalation was a crime that led to the death of 60,000 Americans, hundreds of thousands more with PTSD, and 2 million+ murdered Vietnamese civilians. Not to mention hundreds of thousands of birth defects caused by agent orange and the still ongoing effort to clean up dioxins from the environment.