At my current job, I have been presented with an unavoidable situation in which I must immediately, continually, and indefinitely act in an unethical manner in order to stay employed. Even if I oblige, there is a good chance this could backfire and I'd be out of a job, anyway. Therefore, I am strongly considering quitting in the very near future.
That said, I do not have other employment lined up and am worried about job-seeking without a current job. I have never done that before in my professional life, so I don't know if that will negatively affect my chances during the hiring process. I've already seen questions like this one with highly-upvoted answers that warn against mentioning ethics as the reason for leaving an employer, but I have not found a Q&A that addresses this situation from the perspective of someone who has already left an unethical employer and is currently job-seeking.
I think that answering the interview question of "Why did you part ways with your employer?" with something vague like "Not a good fit" leaves too much to the imagination. Typically a career professional does not choose unemployment before looking for another job, but that's exactly what I want to do, and my conscience is making it hard to avoid.
How should I go about answering that tricky question?
EDIT: The reason why my question is distinct from the question I linked is because there is an additional explicit factor: I will have already quit. It's analogous to asking for a good apple pie recipe vs. asking for a good salted caramel apple pie recipe.