What is legal and illegal doesn't mean anything is right or wrong. Yes, killing someone is illegal, but who's to say it should be illegal if they wanted to be killed, and would be found competent to make that decision?
If the man wanted to,and agreed to be eaten, then why should he be charged? Is there a law saying specifically, that if someone wants to be eaten and you eat them, you will be charged regardless? I don't see that mans family charging him, but I do see the "law" taking it as their "responsibility" to charge him.