I'm here for a job, not to play weird mind games.
It's understandable, but I still can't agree that it leaves you without some amount of ethical culpability. Maybe significantly less than an executive. But still, some. It's more understandable for roles that don't have as strong a position in the labor market as engineers, but I find it a little bit less so for myself, as someone who works in engineering.
I think you (and anyone else downvoting) should read Eichmann in Jerusalem [1]. It's about this exact ethical quandary. I would hope it would change your opinion on these things, but if it doesn't, agree to disagree. And certainly don't expect any sympathy from me or the rest of society.
> checking to see if I'm a disagreeable person who is willing to badmouth somebody generous enough to employ me.
Ah, but you see, the guy I originally replied to is checking to see if you're willing to badmouth companies he dislikes. And if you don't, he will dismiss your application. It's an unspoken rule you can violate without ever knowing you're in violation of it and has a huge affect on the outcome of the scenario.
No reasonable interviewer is going to put you in the position of having to cast aspersions on a previous employer. That's a minefield for all sorts of reasons.
And as other people mentioned, especially in an interview where you're being intensely judged and have to give second thought to everything you say, I'm not about to give anything other than a neutral answer that's supposed to appease most people.