Actually, I was surprised that Calley was still alive. It turns out that he had been living a quiet life in Ohio and Georgia.
It's probably useful to remember what happened. Here's a version from the "apology" story.
Calley explained [at his court martial that] he had been ordered to take out My Lai, adding that he had intelligence that the village was fortified and would be “hot” when he went in. He also said the area was submitted to an artillery barrage and helicopter fire before his troops went in. It turned out that it was not hot and there was no armed resistance. But he had been told, he said, that if he left anyone behind, his troops could be trapped and caught in a crossfire.Not leaving "anyone behind" was a euphemism for killing hundreds of unarmed people. Event though Calley didn't serve nearly the time he should have for the horrific crime, the commanders and politicians who put Calley in that position are the ones who should have been punished more severely.
The same way that Dick Cheney, Paul Wolfowitz, and the people behind the Iraq War should be punished.