Right. D&D has always been based on mythological lore and folk tales. In those stories, good and evil exist. They are defined. They are broken out. Please let's not strip D&D from its foundations. Please don't try to mold and craft D&D into yet another ambiguous fantasy world(s) where these foundational things don't exist.
Literally, the entire world of Forgotten Realms is built on alignment of good, evil and neutral. You have entire planes of existence that exist within these alignments. You have your good realms with your good gods and your evil realms with your evil gods. Each has their good or evil minions. The Material Plane is neutral where everything comes together. Good, evil and neutral all exist within the Material Plane. That is why it is the way it is. It is the entire premise for the entire story. Good and evil are warring in the neutral zone, and neutral is trying to balance them out to make it so that it is even livable.
Seriously. If you strip alignment from D&D, you turn it into every other fantasy sci-fi world/universe. Goblins become aliens, like Twi'leks in Star Wars or Romulans in Star Trek. No. Goblins are an evil race because they are aligned with evil and do evil things like eat and torture people. Same with mind flayers. What, are we to assume, as someone previously said in this thread, that we shouldn't necessarily kill the Illithid tadpoles in our heads because they are technically the offspring of mind flayers? Should we feel guilty about killing them because they are technically children? If attacked by a baby intellect devourer (which apparently most of them in the game right now are maybe supposed to be since they are SO much weaker than true intellect devourers), should we feel bad about killing them?
This is exactly why the game is designed to specifically designate evil as evil. It's so that you can know killing this monster or that is okay and good. You don't have to question it. You don't have to have a moral dilemma about it. Goblins are evil aligned. Their children are evil aligned. They will all grow up to be evil monster adults. There may be exceptions here or there that are REALLY few and far between, but the baseline truth in FR is that goblins are bad. Kill them like vermin before they kill you.
As for tieflings, they may look like devils but they aren't. There is no evil alignment attunement in them. That is one of the main points of the race. They are viewed as evil, but they aren't. That's one of the things that makes them unique as a race from a story perspective. BG3 actually plays upon this rather well. They are letting you know that this entire group of tieflings isn't bad. The kids might be mischievous and thieves, but that doesn't necessarily make them bad or evil. Goblins, on the other hand, ARE EATING PEOPLE. Even the kids. They are kicking corpses and laughing about it and throwing stones at Halsin and talking about killing him, and their adults are cooking Brian the dwarf on a spit, along with others they captured and killed from Waukeen's Rest, and so forth, and the kids are going to partake in it all because they're evil. It's a HUGE difference, and it is all differentiated and split out for us via alignment so we don't have to have moral dilemmas in regards to killing the goblin children. They're evil, like mind flayer tadpoles, dragon wyrmlings, intellect devourer spawn, and any other evil alignment race's children.
