As I interpreted it, someone said adblock may be illegal under existing law because you are accessing a server without authorization. Someone else seems to have argued that this isn't true because adblock doesn't cause anything to happen on the server; therefore, adblock must be legal because adblock only affects the client.
My comment was that this reasoning doesn't hold water. Perhaps the owner states that authorization is only granted to people who don't use adblock. (Maybe there's a splash page that informs the user they aren't authorized to proceed to the next page if they have adblock enabled.) What matters is the choices people make, not that the behavior of the software avoids interacting with the server. Your hands are not clean just because your software doesn't take an action.