Community considerations aside, there's one big reason why you shouldn't post diaries over at redstate.org - you lose your copyright.
I was reviewing this Harry Potter diary over at redstate, which was a republication of an article the diarist had originally submitted elsewhere.
In the comments I see the following discussion:
Erick (one of the directors of the site):
Sir, please be advised that by posting a diary at RedState, RedState.org, Inc. has technical copyright of the material.
Even if you've first published it elsewhere, you lose the copyright. Trevino concurred.
Erick again:
If this has been published in multiple locations, it is most likely the case that no one owns the copyright. The general rule is that the copyright of an article in a periodical, which RedState most closely resembles, is originally copyrighted by the author.
However, RedState has an announced policy that material here is collaberative and held without license by RedState and is presumed to be copyrighted by RedState.
Given the conflict between the held copyright and the fact that this information appeared in a variety of places and the fact that RedState has, on its front page, a clear representation that it holds the copyright of all posted materials other than comments and the fact that there has been no official filing with the US Copyright Office at the Library of Commerce, the copyright would fail.
This policy isn't without precedent - in fact, I even have a group collaborative creative writing website, where participants write chapters of group-created stories. The copyright of the resultant work is owned by my site.
However, the difference there is that none of the original submissions would make much sense without the context of the other submissions. Over at redstate, it really is a collection of diaries and articles that honestly could stand alone.
If you've written an article that you're proud of, and post it at most sites, you retain the copyright. But if you post a copy over at Redstate, their policy maintains that you agree they automatically own the copyright. So if you want to keep your intellectual property, don't post over there.
Whatever floats their boat, but I think it's a poor idea on their part - it basically creates a disincentive for the community to come up with truly great content. (Please withhold the predictably snarky responses to this thought. :-) )