I could even be a threat to the property values of wherever I live, forcing me into a shitty neighborhood.
Unless you own your home, and if society can't force you off the land then you are now damaging your neighbors' property (value).
(not that I think society should be able to force out a property owner, but it does create a minor paradox)
Right, and that's how property values go down. My neighbors no longer want to live near me, so they sell their houses, and they can't sell them for as much because people aren't going to pay as much to live near the 9/11 guy. That, in turn, drives down the property values of my own home, as the neighborhood is suddenly inhabited by poor people and the 9/11 guy.
The other possibility is that I simply wouldn't be able to move to a nice neighborhood because real-estate agents know what would happen if they allowed me to move in to one of their homes.
Sure, when you phrase it like that. But actions will still have natural consequences, and (smart) people are going to consider that when they make their voluntary decisions.
For an extreme example, if I go around saying that 9/11 was a good thing, people are going to avoid me, at best. Depending on how vocal I was, I could have trouble finding a job, businesses and other institutions with a reputation to keep would ban me if they felt it was necessary, and if I was really vocal, I could even be a threat to the property values of wherever I live, forcing me into a shitty neighborhood.
Sure, it's not a good thing, and it is technically possible in a Voluntary society. But that's exactly why if, for no other reason (such as empathy or a lack of insanity), people agree 9/11 was bad. They're disincentivized from rejecting cohesion to that extent because it would make them outcasts.
But the bottom line is that it's more important for them to have a choice than it is for them to think 9/11 was bad. Let them dig their own graves if they wish.