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.
The idea that Marlin should just chill out like a stoner turtle, or let go like an amnesiac tang fish, and let Nemo find his own way in a world that is systematically trying to kill them, is just plain dumb.
Plus, the two characters who give him this advice are easily the least trustworthy of the lot. Dory can barely remember her own name, but Marlin is supposed to believe that she knows when is the right time to "let go." Is she even a parent? She tells him this after they've been eaten by a whale.
And this dingus is getting her own goddamn movie.
As for Dude Crush (the stoner turtle), he's just lucky his kid, Squirt, isn't eaten by a passing shark or knocked unconscious when spinning out of the East Australian Current. And yet Marlin is supposed to take that as a good example of parenting?
Oh, and remember at the start when Marlin loses his shit when he learns his kid is going to the drop-off, worrying that Nemo would get away from the rest of the class and something bad would happen? That part when we all rolled our eyes? Yeah, that's exactly what happens.