A good software written to spec is by definition ethical. It is unethical to write bad software, not evil one. But if you write bad software - nobody should hire you anyway.

> A good software written to spec is by definition ethical.

Even if the spec specifies unethical behavior? Sounds like passing the buck.

Or what if the spec itself isn't well defined, and leaves many undefined states and holes that the developer has to fill in themselves?

If a lawyer submitted a brilliant and conforming but racist or unethical argument to a court, the lawyer can still be found to be unethical. Just because you're following the rules, doesn't mean that you're doing the ethical thing.

Even if the spec specifies whatever unethical behavior means. That is problem for the guy using the software not the one making it.

Get the job done, get the money, get out.

If you want to waste precious time of your life wondering whether something is wrong - be my guest. But don't impose it on people with better things to do.

Careful - this line of argumentation can also be used to allow yourself to do some very, very evil things in life.