The problem is that if engineers in the US don't take the job then someone somewhere in, say, Asia will. Ethical rules are not the same everywhere. You can already tell this by looking at experimentation with stem-cells, cloning, et cetera, which is happening faster in Asia than in the US because of regulations.

Also, refraining from building these systems means that other countries get ahead of us. Besides being an economic disadvantage, this could also threaten security.

So I do agree that engineers should adhere to ethical guidelines, but they should be considered in a global context.