Another possible solution could be to take "akusala.m. . . pahiina.m" as an
accusative absolute and translate the passage as:
And if the unwholesome were given up, that it should lead to pain and harm,
(then) I would not say thus: monks, you should give up the unwholesome.
There can be variations in the translation of the accusative absolute: when
the unwholesome is given up; while the unwholseome is being given up; etc.
An example of the use of an accusative absolute is found in the following
passage:
vandite ca panaayasmataa mahaakassapena tehi ca pa~ncahi
bhikkhusatehi sayameva bhagavato citako pajjali. --- D II 164
And while (the feet of the Blessed One were) being venerated, moreover, by
the Venerable Mahaakassapa and the five hundred monks, the funeral pyre of
the Blessed one burst into flames just by itself.
"vandite" is in the accusative plural and should be read with "bhagavato
paade" from the previous sentence.