Yes. I believe arguing for the right of prisoners to receive free food consistent with the American Civil Liberties Union mission statement, because it is a basic human, or civil right. Regardless if a person is in prison, or not they deserve to be treated with basic human rights. No exceptions.
Prisoners, while incarcerated, are still Americans and need to be offered protections. Prisoners need to expect basic care and protection, consistent with the ACLU mission. Food is a part of this. It can be argued that food while in prison is 'free', but should really be looked at as a basic right for those who otherwise would have no other way to garner nourishment.
The American Civil Liberties Union mission statements says it is there "to defend and preserve the individual rights and liberties guaranteed to every person in this country by the Constitution and laws of the United States." Given the statement I would say arguing for the right of prisoners would fit into their statement.
The American Civil Liberties Union mission statement is simply stating what the nations Bill of Rights already says, and that all citizens have certain rights that are naturally theirs and will not be taken away. Prisoners being given free food is not a part of this mission statement at all.
No, arguing for the right of prisoners to receive free food is not consistent with the American Civil Liberties Union mission statement, because the ACLU's mission is primarily to defend free speech. It is not to defend the comfort of criminals, or the increased socialization of our country. The ACLU should stick to what it does best, which is issues of free speech.