The Little Mermaid of the New Century

Ellie was a purple-tailed mermaid. Among mermaids, purple-tailed bloodlines were the most noble, so her birth mother took great care to teach Manli: "Men on land are all dangerous. Never go near the land." That almost set off the rebellious streak in Ellie's mind, but luckily, her mother continued, "Except in spring." "..." Ellie asked, "Why is spring okay?" Her mother said, "Because spring is the season for reproduction. We go to warm, shallow waters to lure men. A week later, if you lay eggs, those are male offspring, and you leave them for the men to hatch. If you're carrying female offspring, then they're born live, and you have to swim back to the seabed to give birth. The rest of the time, kill every man you see." Ellie asked, "Why kill them?" Her mother said, "If you don't kill him, he'll capture you and take you inland, beep, then beep, then beep. Ahem... That's just how the world is. Even down on the seabed, we have to fight sea monsters, let alone on land. They have two legs to run on. Where are you going to find water to swim in? So, do you kill them or not?" Ellie replied firmly, "Kill them." Her mother added, "If you come across a young male, don't kill him." Ellie asked, "Why?" Her mother said, "Save him to reproduce in spring. Wiping them all out would upset the ecological balance." Ellie said, "...Oh." So that's okay? Is this setting really all right? Could someone please do something about this world's System or whatever the Main God is?!