Just because there is debate surrounding a subject does not mean that the debate is reasonable. In many cases, it is more likely that the people doing the debating are being unreasonable. The global warming debate is a good example of this. One way of being unreasonable is misunderstanding each other's terminology. This happens a lot in free will discussions, and I suspect it is also happening here. A way to get around this is to taboo certain words.

(Also, 'evidence' can have a variety of meanings and not all rational debates strictly require evidence. Mathematics proceeds entirely without any kind of evidence (in fact, evidential reasoning is discounted in mathematics)).