I think it will be interesting to see how this plays out in practice. As Paul Thornton admits, he is the letters editor, but not a science expert. I'm sure that through the years many trollish letters on various topics have been eliminated from letters to the editor pages without getting this sort of blanket comment published (even though analogous policies may have existed). But I think it would be detrimental to the public discourse if we are all isolated to our own private echo chambers.
As an alternative example:
In a recent exchange with our local denialist in residence, retired professor Don Easterbrook, The Bellingham Herald published all of the items below:
His influence with right wing politicians: http://www.bellinghamherald.com/2013/03/26/2939145/retired-wwu-professor-a-global.html#storylink=misearch
A public stand by members of his former department refuting his denialism:http://www.bellinghamherald.com/2013/03/31/2943649/wwu-faculty-find-overwhelming.html#storylink=misearch"We, the active faculty of the Geology Department at Western Washington University, express our unanimous and significant concerns regarding the views espoused by Easterbrook, who holds a doctorate in geology; they are neither scientifically valid nor supported by the overwhelming preponderance of evidence on the topic."
And even responses by Easterbrook and letters to the editor by his supporters (as well as detractors).
I believe that there is a fine but important line between regulating real trolls and bringing viewpoints to the public attention that need to be openly aired and discussed. While the denialists themselves are probably beyond convincing, it is still important to understand what they see as effective messaging to the general public so that we can plan messaging that addresses those very issues in a scientific manner.