Legally Sam would not be raising Lucy
As much as I found Sean Penn's performance quite moving (and Dakota Fanning's performance quite nauseating), the film is a outcry of illegitimate pretenses and a fake ending.
Sam would never had been allowed to raise Lucy in the real world. After all, he was mentally challenged. What is going to happen to Lucy when she turns 14 and needs guidance through high school? Is Sam going to be able to tutor her though the tribulations of being a young woman? Sex with boys? Mean girls in the playground? I don't think so.
As Roger Ebert said, this film was all about feelings, but in the real world feelings mean nothing. Sam should have allowed Lucy to have real parents to look after her. Just because your sperm created her, don't make you the father. I am adopted- my adopted parents raised me. Did I need my original parents to raise me just because they created me? Nope.
*1/2 out of ****
(oh, and a retarded guy would never be allowed to work at Starbuck's)