Common Good?

I was recently asked about the common good in regard to morality. Here's the brief response I wrote. It's unfinished.

I used to be a utilitarian; I was the guy who, when asked the question about who you would save on the train tracks, the one guy or the group of people, I chose the group. Then I became interested in history. I read about people such as Hitler and Stalin, and I realized that this whole idea of “the common good” has been the justification for nearly every mass murder in history. I realized that when morals are subverted to whatever “society,” if such an entity can exist, deems to be the common good, then morality becomes subjective. What was good one day can be bad the next. Since society is simply a collection of individuals, the common good can only truly be defined by an individual, such as Hitler and Stalin. Anything they deem to be moral is moral. Who can question that? Who would dare question the common good? I now look at morality on a rational, individual basis. When confronting the question about who to save, I ask the question, “of value to whom?” Who is the man on the track? Who are the people in the group? I recognize now that value and morality doesn’t exist at the collective level, but the individual, and my moral decisions are now based on this principle of individuality.