When he takes Nemo to school for the first time and learns that the teacher is taking them to the drop-off, Marlin freaks the hell out and races after them. He tells Nemo's teacher that his son could easily sneak off and get hurt, that he's not ready for school yet, and a bunch of other crap that makes us roll our eyes at how demanding a father he is and how unfortunate Nemo is to have such a hardass dad. We've all seen those overprotective parents, and we always want to tell them, "Holy shit, dude, you have to settle down. Your kid will be fine."
But Marlin is absolutely right, because everything that happens during the film should convince him that instead of letting go, the exact opposite is true.
The Actual Moral:
From the moment the film begins, Marlin has to deal with so much shit it's a miracle he doesn't strap Nemo to the anemone and keep watch 24/7. Let's have a recap:
1) His wife and 99 percent of his children are eaten alive by a barracuda. 2) His son, on his first day of school, ventures away from the class and is kidnapped by an Australian dentist (Parents: Beware). 3) He is pressed into joining a "Fish Are Friends" AA-style club run by sharks, who are not sticking to the program. 4) Said club's leader, Bruce, tries to eat him. 5) He is almost blown up by underwater mines. 6) He is eaten, but not digested, by an angler fish. 7) He is shocked unconscious by jellyfish. 8) Again he is eaten, but not digested, this time by a whale. 9) He survives a spinning "vortex of terror." 10) Once more, he is eaten, but not digested, by a pelican (for a change).
He's been in and out of more mouths than Ron Jeremy.