What Xanadu has that others don't: When responding to any argument
(for or against something), you will be able to comment on each and
every relevant sentence. The document you are commenting on will
automatically link to your analysis. Whether readers of the document
see your comments or not is up to them. They will have filtering tools
to include or exclude whoever they want. That is their decision to
make. Thus every possible viewpoint can be heard and can cross-comment
on each other as much as desired.