I don't really know much about the Vietnam war - but I do know a little about the chemical "Agent Orange". It was mass produced (although not created) by the chemical research division of the Monsanto Corporation (they didn't start up as a genetics company, and indeed, Monsanto still make quite a profit with its chemical arm of the company).
Now, I've heard from people who say that it was all a conspiracy to poison the Vietnamese. My mother believes this as well. But the fact of the matter is that they started dropping this years and years before the war was over - if they knew it was poison, they wouldn't have sprayed so much so soon, because then the press would have gotten wind of it. Plus, the objective of the US was to secure South Vietnam - this Agent Orange stuff spreads, dioxins spread, and they certainly didn't want to poison their allies. They didn't really know what it could do at the time - medical science wasn't as advanced then as it is now, they probably didn't know it was so toxic to human beings. Hell, quite a few US soldiers got really sick from handling the stuff. They just thought it was a really good defoliant.
Should the US pay compensation? Sure. The companies who manufactured the stuff have already paid compensation to soldiers who got sick. The science on the effects of dioxins is pretty solid But I suppose they didn't know it was a poison.... and if they didn't know what they didn't know, was it really negligence?
Yes Agent Orange is bad and it has caused some birth defects. But friends of mine have been to vietnam - most children are born without such defects. Vietnam isn't a nation where everyone under the age of thirty looks strange. Agent Orange has raised the rate of birth-defects and abnormalities, and in areas which recieved multiple sprays of the stuff, the rate of defects is quite high. Also, US bases where some of the excess chemicals were buried, also have high rates of dioxins.
Should the US pay compensation to the vietnam government? Hmmm, maybe. But they probably won't. The Vietnam government has already identified areas which have high levels of contamination, so the problem should stop pretty soon. Should the US pay money to children who have been affected by this disease? Well, if they were nice, sure. But no government is "nice". The most you could hope for is help cleaning up the remaining sites.