Except, you know, there's the law I could refer to.

Or like two months ago when the guy who hired me wanted me to ship software that was clearly going to explode in production and I told him that I'm not interested in having that kind of disaster on my conscience and that he would just have to deal with the fact that its going to take longer to ship.

Saying no is about having a spine, not about being able to hide behind something that you can hold against your employer. Maybe they're right. If you are incapable of making decisions in a professional fashion, you should not call yourself an engineer.

Ethics can be a tough thing, and it can take more than just a spine to refuse unethical work. Identifying something as being unethical in the first place can be a challenge for someone new to a discipline. Having a professional community that explicitly teaches and tests you about their Code of Ethics gives you a framework and support network to help you with those decisions. It's also kind of a cultural thing. Having transitioned from chemical engineering to artificial intelligence, I'm amazed at the different cultures regarding ethics. Not having an entity responsible for defining the code of ethics in my new discipline, and the lack of community around it, has made it much more difficult to discuss and challenge the ethical decisions we make. Most of the time, when I bring up ethical discussions, my classmates and professors respond with "that's not our responsibility". When I ask whose responsibility it is, the answer is always "someone else's".

This is simply not true for all tech companies. I've had instances where I said no due to asks being not in line with company policies and we changed course to tackle the problem another way. I work at Microsoft and there's severe rules against retaliation should your boss penalize you for something like this.

For every Microsoft, you have 50 pretty much any advertising network, random consulting firm or other company that doesn't give a shit.

Exactly, having the backing of a profession that expects and mandates you uphold its Code of Ethics is a very powerful thing. Refusing to do work you deem unethical is much easier when you have the support, expectation and legal obligation to do so.