This is what Dowding and Churchill apparently said on the subject:
"After dinner, they discussed the topic about the morality of shooting parachuting Luftwaffe pilots. Dowding suggested that German pilots were perfectly entitled to shoot RAF pilots parachuting over Britain as they were still potential combatants (i.e., going back to a new aircraft to conduct another military mission), while RAF pilots should refrain from firing at German pilots as they were out of combat and would eventually become prisoners of war once they landed on British soil."
But not if they bailed out over Ireland.
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And I hafta wonder if "potential combatant" is really a good yardstick to use. On the ground and using the standards of the time, any able bodied male between 16 and 60 was a "potential combatant." I assume it would not be considered moral to shoot all of them during a war.