There seem to be a few other options that wouldn't be quite as unprofessional.
The interviewer is saying that at the end of the process, the offer isn't going to match the interviewees expectations. If that isn't going to be acceptable, then it's okay to end the interview right away. "Walk out" is a bit or a harsh way of putting it, even if effectively, that's what the interviewee is doing. As the interviewee, I would clarify the rough terms being offered, and politely decline. I would then transition to say that the company was still interesting, and that if something open up in the future, maybe when my skills and experience matched their expectations for a different role, I'd be interested in talking again. I'd keep it very friendly, shake hands, and leave them with the impression that I was someone they'd like to speak with again. This way you've established a relationship, and negotiated part of the next interview.
Just walking out isn't a good negotiation technique in this case. It does have its place--but not here, precisely for the reason you mention: there will not be future interviews. It's nice to think of movies where someone effectively spits in the face of the interviewer, and ends up getting the offer. If this does happen, it doesn't happen for low level positions or future engagements. "Hey Bob, remember that guy who just walked out? I wonder what he's up to...". Walking out shows that your highly desirable value will go elsewhere. If they don't see your value now, walking out is just saying you're an unprofessional jerk, they'll throw your resume out, and the bridge will be burned.