Here's the problem:
I maintain that when a Libelous statement is offered without any support and as a fact, instead of an opinion, it should be deleted, as none of the above arguments apply:
Bold emphasis mine.
You cannot determine whether the statement is libel and neither can I. The correct word to replace "Libelous" above would be "Questionable".
When you delete a post because it's "libel", you are effectively deleting it because it is "not true", and put the site in the position of asserting that all undeleted posts are "true".
Do you any inkling of the size of that particular can of worms?
I think it's possible to make a case for allowing deletion of "untrue" statements in non-stock threads, with the stated understanding that the chairperson assumes all potential liability that may arise out of his doing so, but not only is it dangerous to the site to allow that kind of editorial control over stock-specific threads, it's potentially dangerous to people with current or potential financial stakes in the stock, in addition to being just plain *wrong*.