I've explored similar ideas in the past. One possibility I explored was breaking down claims like 'Guantanamo Bay should close' into moral claims plus factual claims, eg 'Guantanamo Bay practices torture' plus 'torture is wrong'. This could be further broken down until you had a set of moral axioms and a set of basic pieces of factual evidence, and a set of syllogisms linking them together.

Different people would indeed have different value systems and also give different degrees of credence to different sources. So the goal would be to end up with a crowdsourced tree of moral & factual claims, and individual users could then decide which claims they agreed or disagreed with to come to their own conclusion on the topic.

(Look up 'argument mapping' for academic exploration of the concept).

My thinking now is that most online political arguments online are really about tribalism, not finding the truth. If you did have users who cared about the truth (and who could consider other viewpoints), you wouldn't need a fancy product: a simple web forum would suffice.

But do drop me an email at isaac@i.saac.me if you'd like to chat more.