Heartwarming / Mermaids: The Body Found

• The Real Life co-operation between fishermen and dolphins in helping them capture fish is definitely a Crowning Moment, showing co-operation that only two sapient, intelligent species could engage in. If that activity doesn't prove dolphins are near-equals with humans in intelligence, nothing won't.
• Like many mythological beings^note coughVAMPIRESANDFAEcough, merfolk-like legends were rarely benevolent, with very few exceptions . Like any historical conflict between different groups, there was probably mutual aggression from both sides, leading to human legends of dangerous mermaids/sirens/etc. But the scene with the merfolk approaching the submarine and putting its hand on the glass (in a clearly peaceful gesture), implies that some merfolk may have made peace with us, possibly giving rise to more benevolent mermaid stories. Maybe the merfolk are sick of fighting and want peace.