Some were, many weren't. That said, there was a lot of hostility in the public back then toward returning vets. There was a lot of false propaganda spewed by haters that claimed our troops were committing crimes they never committed, and sought to demonize them at every turn. Sadly, a lot of people fell for that false narrative and did express anger toward our soldiers. Some, like actress Jane Fonda, portrayed the North Vietnamese and their partisans in the South as noble "freedom fighters" that were trying to "liberate" their land, and American soldiers as brutes, when the forces of the North committed vile atrocities, not only against American Prisoners of War, but also against their fellow Vietnamese!
After the war, the government of the North institutionalized persecution of millions of Vietnamese citizens, separating families, beating, raping and murdering untold numbers in so-called "reeducation camps". If anyone deserves to be spat upon, it was not American soldiers, but the vicious, savage elements that represented the North.