I know the LFG incident got a lot of people fired up, but it's not beyond understanding. The people that organize the event have a lot on their plate, up to and including celebrities and visitor safety concerns. Even the people on the bottom of the totem pole are run ragged keeping things together from two days prior to the doors opening until long after they close. (I've known someone who's done it; the work load is absurd at the best of times.)
It's not unforgivable that the attendants were less than helpful; most of them would have been on a short fuse to begin. It also says something that a board member came down to personally apologize and set things right.
What likely lead to not being invited back was calling and leaving messages three times per week for six weeks. Now, I admire and respect the LFG staff, don't get me wrong; but, for any office handling that volume of planning and organization, that would have given them a bad taste for whomever was calling. It may have been too harsh in our eyes, but for someone in that position, breaking relations with the responsible party would have seemed the simplest and most effective course of action.
I'm not saying that what happened to LFG wasn't unjust, but please understand: They were one client among many, many others. These sort of things are going to happen. It's not right to hold a grudge against the organizers and patrons of DragonCon because of one unfortunate incident.