Personally, were I attending Worldcon, I would be deeply uncomfortable with being on panels with Walling or attending panels he's on. This is not a feeling that is exclusive to me! I know he's on panels, in fact, because a friend of mine was supposed to be on a panel with him and decided that that was not okay. My friend e-mailed the head of programming "and told them in polite but no uncertain terms that I will NOT do a panel with this person, based on the well documented events of Readercon, but that I leave it up to them as to how they choose to resolve this."
I was like well done and also friend, that is a great idea that I would like to share.
So. If you're uncomfortable with a serial harasser representing our community at Worldcon - if this means you will avoid being on or attending certain panels - you might like to let Programming know. They might be interested.