These are in fact the same thing. It is because an engineer can be held liable that results in them being
willing to say no. In general, they probably won't be prosecuted, but a common reason for this is that there will be written records of engineers telling management that there are concerning risks. This also results in the job of a Professional Engineer, who is a person who legally puts themselves on the line. They get paid very well and for good reason, they have a lot on the line themselves.
I suspect that a big reason CS is not held to the same standards is due to abstraction and that it is still new. But we do live in a time where bad code can get people killed (control systems are the easiest examples), just as building a faulty bridge will. I just hope we don't need a Tacoma Bridge to cause change. Obviously it is harder to figure out things that are more abstract like Social Media (can provide both good and harm).
But I'd say, you can always say no. If you're not saying "no" now, that's still a choice you've made. A job is very persuasive, and I'm not saying you're bad for just keeping your head down, just that people should consider where they'd draw the line. The line is personal and different for everyone (which is okay!). Having taken traditional engineering courses, I'll note that ethics is frequently discussed and you're likely to be told you should try to define your line before you asked to cross it. If you don't, you'll likely to cross the line without knowing, as you just didn't know what it looked like. You can always redefine the line as you get more resolution (it continuously updates) but it's much harder to say "no" when you haven't given it much thought.