What should forum policy be on defamatory posts?

I'd add that, historically, some proponents have had 'open season' on certain high profile skeptics. Decorum on all sides would be desirable.

While I agree that some decorum would be desirable, I must say that the playing field is hardly even. Psi research and evidence has to contend with automatic accusations of deception and/or delusion. The media and internet are dominated by sceptics. This forum is not a microcosm of the world at large - for some it is a refuge where both sides can be discussed. Some of those high profile sceptics (yes, I do mean Randi in particular) have been lauded in the media without question so you shouldn't be surprised to see some attempt at redressing the balance. 

People like Dawkins and Krauss are scientists and should represent free and open enquiry but they don't. They have the stage because of their scientific status but choose to promote a philosophically dogmatic agenda, proclaiming in absolute terms that psi, along with God and any kind of spiritual belief should be eliminated from consideration. That is not an honest use of the scientific platform they have been afforded.