It is currently possible for visitors to block moderators. This is incredibly dangerous, especially for large public events where users are expected to abide by a certain set of rules. As it is, the only ways to handle a user who has broken a space's rules are to talk to them or ban them. Since banning a user is analogous to throwing them out of the event, it is understood that this is something to be used sparingly, and wouldn't be warranted for more minor infractions, but it's not possible to handle more minor infractions if moderators cannot speak to a user, especially since there is no way to tell if you have been blocked.