I strongly support the notion of whipping up a DSL for argumention targeted at LessWrong readers. Philosophy and law argumentation tools seem to be targeting users without any math or logic who demand a graphical interface as the primary means of creating argument. My guess is that LessWrong readers would be more tolerant of Bayesian math and formal logic, the necessity of learning a little syntax, and only exporting a graphical representation.

Features might include:

• Compose in ordinary ASCII or UTF-8
• Compose primarily a running-text argument, indicating the formal structure with annotations
• Export as a prettified document, still mostly running text (html and LaTeX)
• Export as a diagram (automatically layed out, perhaps by graphviz)
• Export as a bayes net (in possibly several bayes net formats)
• Export as a machine-checkable proof (in possibly several formats)

I'm currently learning noweb, the literate programming tool by Norman Ramsey.