Just logic and/or critical thought in discussion. It doesn't have to be formal.
Well, I agree.
All to often, however, people are met with the "LINK?" accusation to support their claim, and to be a bit blunt, even in this this OP, the notion of supporting evidence is a key requirement for the entire forum premise.
I don't disagree with this idea, or the forum. In fact, I would find it refreshing.
However, logic means different things to different people it seems, and a conclusion, chased down from a premise, based upon evidence provided, does not seem to qualify anymore.
So, I personally (there is no force of requirement obviously) would like to see limits placed upon the sources of information that can be used.
There are far to many biased sources (both left and right) and to many agenda's to know what is acceptable and what is not.
Hell, our esteemed professors in our universities require the students to use only those sources they deem acceptable.