There are a couple of industry sectors that I would rather not write software for, ever. The most important ones are:
There are many others, the common denominator being that I do not believe these activities have a positive impact in our society.
I make this list public as an invitation to you, software developer, to examine the social and ethical consequences of our professional activity.
It is undeniable that programmers have an increasing impact in our world through the software we write. If our only concern is doing our job right but we not mind about the consequences of what do, we risk becoming mercenaries.
At any point I suggest that my list is universal, different persons have different thresholds and sensibilities. It is nonetheless important that you ask yourself whether you are being consistent with your own values and principles, and perhaps, make your own list.