THERE ARE no victory parades, no brass bands, no cheering crowds when the soldiers come marching home from Vietnam.Most of the 4.2 million veterans of the Vietnam war have slipped quietly back into society — so quietly, in fact, that it is almost as if they had never gone away.They return one by one, not by regiment or division as their fathers did after World War II or their grandfathers after World War I, and one by one they go to work or to school.The society they return to is not such as to encourage them to speak about their experiences or be proud of their veteran status.They are not greeted as heroes; no one offers to buy them a drink, as people once did for the veterans of Normandy and Iwo Jima.Affluent America shows no signs of a wartime society. The Vietnam veteran often feels his uniform is out of place in themiHct r\f all thic corrrincr nnl\7