Almost every single aspect of the lore about goblins is actually based on them and how they view masculinity. If you are a man who isn't a goblin in mannerism and looks they will either call you "gay" or seek an opportunity to commit a violent hate crime against you.
They try to multiply to overrun civilization and a naive person might think of sparing their children but they are not thinking of how they will grow up to rape and wipe out anybody different to them.
They are basically parasites who just want to take over and exploit the whole earth until it becomes Mars, just like the Goblins from Goblin slayer.
Just like the goblins from goblin slayer people are naive about them and their biggest strength is that they exploit the empathy of compassionate people to be allowed to thrive in the world.
If you show empathy, possibly even to their children it just becomes a chance for them to cheap shot you. They want to weaponize and use their children as a weapon to take over civilizations until the Earth is infested and dying.
In the end the only good goblins are the ones that never show their faces to the light of day. There isn't a single reason to show them mercy.