A person shall not be convicted of an offence under section 2 of this Act if it is proved that the giving of the performance in question was justified as being for the public good on the ground that it was in the interests of drama, opera, ballet or any other art, or of literature or learning.

It is hereby declared that the opinion of experts as to the artistic, literary or other merits of a performance of a play may be admitted in any proceedings for an offence under section 2 of this Act either to establish or negative the said ground.