For the same reason that it's unacceptable (to others) that the choice be left to the whim of the Censor. Some past Censors have misused validation to stop polls they don't agree with. Some pollsters have misused polling to try to circumvent the law (and tried to use the private nature of the poll to allow the citizens to vote yes without fear of being identified as approving circumventing the law). Neither should be allowed. My procedures, which donsig promises to challenge legally (how I'm not sure) allow the citizens to overrule the Censor on disallowing a private poll, and the Censor to overrule a pollster who misuses a private poll.