As far as I can see the argument is already over if the anti-XT crowd feels it is so certain to lose any fair contest that it will resort to tactics like this.

Seriously.  They screamed all rational discussion about ending the block size limit to a standstill even though ~75% of the users and an even greater fraction of the miners are solidly in favor of >1MB blocks, and now that they are facing an actual implementation of a client that will hardfork to >1MB blocks they're trying to sabotage the consensus process rather than allow consensus to be decided by adoption? 

At what point do they admit they've already lost?