Back in 1985 I made a decision that I would no longer work on weapons development projects. Prior to that time I had worked on a software for the B1 Bomber. At the time I was a Christian and I didn't have a problem with it. In fact, I felt that what I was doing was patriotic and therefore good.
I came to realize that what I was doing (building things meant to kill people) was wrong. But I came to that conclusion in kind of a round about way. I came to that conclusion because the Bible makes it clear that Christians are morally obligated to care for the poor. And through research about the causes of severe poverty I found that war is the leading cause of poverty. And so I started believing that war is wrong and therefore making weapons is wrong. If I had been a Buddhist instead of a Christian I could have come to that conclusion faster because the third precept of the eightfold path is "One's way of livelihood should not harm in any way oneself or others; directly or indirectly ".
There are many way was to earn a living that are despicable and bring harm to others. Slave trading and use of slaves is one of the uglier blemishes on US history (not to mention other countries). Yet today people make a living in ways that are just as ugly. Dealing drugs is one of those ways. If you are a drug dealer your customers are basically your slaves. They will work for you, steal for you, give their fortunes to you, leave their families for you, maybe even kill for you and eventually die for you. And let's not forget the cigarette manufactures. I could go on but you get the picture.
How can people make a living in such despicable ways? It's because they value money more than people. The love of money is the root of all kinds of evil.