Well, this is a conservative forum run by conservatives. Therefore the posts they censor are things they don't want you to see.
I just assume a deleted post was an outstanding rebut of a conservative positional weakness that conservativism can't figure out how to answer. If the censors don't want to leave that impression, they should leave the post undeleted so that our own individual minds can assess its quality.
Posts are primarily deleted for being violent, racist, obscene or for containing content that is sensitive now that we are at war.
If such posts are not deleted, others use them to show how terrible FR and the people who post on it are. Frankly, I'd prefer it if they were left up with a note from the moderator attached that FR rejects their point of view.
But this site is private property. Those who don't like the way it is run have the option of starting their own site which will be run by their rules.