What is the meaning of the term "monstrous proposition"?

McIntyre J. referred to Lord Mansfield's 18th century use of the term "monstrous proposition" to describe the suggestion that a Governor acting by virtue of Letters Patent under the Great Seal was entitled to be despotic, being free to spoil and plunder with impunity. He then cited with approval the well known case of Roncarelli v. Duplessis 1959 CanLII 50 (SCC), [1959] S.C.R. 121, and Rand J.' s observation that there exists a general presumption in legislation and regulation that powers given by legislation will be exercised in good faith and without improper motives (my emphasis), saying (at page 140): "...there is no such thing as absolute and untrammelled "discretion"... "Discretion" necessarily implies good faith in discharging public duty; there is always a perspective within which a statute is intended to operate; and any clear departure from its lines or objects is just as objectionable as fraud or corruption" (again, my emphasis).