It appears that jurors are not allowed to be told that they can ignore the law and thus use their right of jury nullification.
The contrary principle contended for by Mr. Manning, that a jury may be encouraged to ignore a law it does not like, could lead to gross inequities. One accused could be convicted by a jury who supported the existing law, while another person indicted for the same offence could be acquitted by a jury who, with reformist zeal, wished to express disapproval of the same law.
But recognizing this reality is a far cry from suggesting that counsel may encourage a jury to ignore a law they do not support or to tell a jury that it has a right to do so.
Since they're apparently still allowed to use this right, only not be explicitly instructed in court that they can use it, doesn't it produce the very problem mentioned above by Mr. Manning? I.e., in any particular trial one juror may have prior knowledge of the right of nullification, in which case the jury may use it; while all other juries will carry out their obligation ignorant of it.