כל בן נכר לא יאכל בו
שמות יב – מג
Do not give a Meshumad [Jew who doesn't believe] to eat from the Korban Pesach
In the time of the Bais Ha`Mikdash, when there is a Korban Pesach.
Males and females.
Since the purpose of the Korban Pesach is so we remember the miracles we saw in Egypt and that we entered under the wings of the Shechina and that we entered into a covenant of Torah and belief, it is not appropriate to give from the Pesach to someone who represents the contrary, who has left all and denied the faith. The sefer Ha`Chinuch states that this reason is so strong, that we would have known it without a Pasuk.
If one feeds it to a Meshumad
The Sefer Ha`Chinuch states that one does not get Malkos, because he has not transgressed through an action but rather through inaction. However, the Minchas Chinuch takes issue with this, asking that one can transgress with action, by forcing it down someones throat or perhaps by giving it to the Meshumad.