E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Ventilate a Subject (To).
To moot it, to throw it out for discussion that it may be winnowed or sifted. To ventilate a room is to let air and light into it, to drive away bad gases, etc. So in ventilating a subject, light is thrown on it, and all that is false, extraneous, or doubtful is blown away.