This is one of these "maybe true in theory" but counter productive arguments.

Irregular migration has been on the rise for many years and the ratio of success is high enough that people risk it regardless of whether or not there are planes looking for ships in distress.

But there is another reason why the Italian government doesn't want these planes flying: they are unwelcome witnesses to illegal pushback operations that the Italians and Maltese (and Frontex) are doing in cooperation with Libyanese mafia militia.