What would the pros and cons have been if America had withdrawn from the Vietnam War just after the Tet Offensive in 1968?

With the benefit of hindsight, it seems clear that there
would have been no real cons to withdrawing from Vietnam after the Tet Offensive. 
However, US leaders would have had a hard time realizing that at the
time.

At the time, withdrawal would have seemed like an
admission of weakness.  US leaders would have felt that they were losing credibility
with their allies around the world.  These allies would have felt that the US might
abandon them if it would abandon Vietnam.  This would have seemed like a compelling
reason to stay at the time.  In addition, there was still hope and confidence that the
US could win the war.  Withdrawal would have precluded
this.

In hindsight, we know that the US would withdraw from
the Vietnam War 5 years later.  This did not lead to a loss of global confidence in the
US.  Withdrawal in 1968 would probably have not caused such a result either.  If the US
had simply withdrawn at that point, large numbers of human lives and huge sums of money
would have been saved.