As some readers have pointed out, there is a response to the WSJ editorial here.
One point that I’d like to re-iterate for the umpteenth time: our articles have been purely critical; they do not propose any view of climate history. I am intrigued by evidence of past warmth, but have not attempted to argue this position. On the other hand, I do not think that any of the supposed refutations of the existence of the LIA and/or MWP are valid.
This applies not just to Mann’s hockey stick, but to earlier work such as Bradley and Jones  on the LIA or Hughes and Diaz  on the MWP. I have not discussed these works on this site or elsewhere, but I’ve collected nearly all the data pertaining to these studies (which is always time-consuming), studied the articles in detail and find them very unconvincing. If I’m correct in my view that Hughes and Diaz  (for example) does not refute the existence of the MWP, I do not jump to the opposite conclusion, that, ergo, the MWP exists. All it really shows is that the IPCC did not check Hughes and Diaz  either.
As to the supposed impact of new data in changing views, if you actually look at the data used in the Mann hockey stick (or Hughes and Diaz, for that matter), they didn’t use much proxy data that wasn’t available in 1990. Remember that their proxy reconstruction ends in 1980 and we’ve heard this strange excuse from Mann that they must rely on proxy work done in the 1970s because the data has to be obtained in difficult and costly expeditions using "heavy equipment". It seems to me that the changing interpretations owed more to a desire to "get rid of the MWP" (as one climate scientist is reported to have said to Deming) than to any new data.