There are a number of SWJ articles on this question and two caught my attention:

1) In 2009'A Better Understanding of the Vietnam War'byColonel Gian Gentile and there is a telling quote:
...the war could [not] have been 'won' in any meaningful sense at a moral or material cost most Americans deemed acceptable.
Link:http://smallwarsjournal.com/jrnl/art...he-vietnam-war

2) In 2011 'Vietnam Postmortem: A Senseless Strategy' by David Maxwell, that is a pointer to a Parameters article by Colonel John Collins. This led to thirty-five comments. Amidst them is one by Ken White, cited in part, with my emphasis:
If we cannot discuss history and current activities then we may have to fight them again as you say -- but I do not believe it will be a like it or not problem. It will be a choice on our part. I for one submit that Vietnam was a mistake in all aspect
Link:http://smallwarsjournal.com/blog/vie...eless-strategy