Adults can be victims of difficult circumstances, but children are the ones who have no choice at all. I can sympathize with young parents struggling, but at some point personal responsibility has to come into the picture. If you know you aren't in a position to provide a safe and stable life for a child, why intentionally have or keep the pregnancy? Abortion and adoption exist as options. Once you decide to raise a child, the child shouldn't have to pay the price for your choice. I can empathize with the parents' circumstances, but my sympathy doesn't outweigh the harm done to the child.

I see a lot of people hating on Mokhyeon's parents, but honestly, I understand the parents and their actions.
They are very young parents, perhaps even students themselves (I don't remember) who were abandoned be their own parents with the very high responsibility of taking care of a baby, without any money I guess.
They probably thought that it would be easier to take care of Mokhyeon, they were probably very optimistic, imagining making their own money, raising the child well. But let's be realistic, it can't go that well. The mother is suffering from post partum depression, and can't seem to get out of here (seeing a therapist isn't always possible for everyone), the father works all day.
They probably also hate each other and resent Mokhyeon (even if he's innocent) as they were young people with dreams on their own. And having a child is breaking every of this dream.
I believe the best solution would've been to abort Mokhyeon (sorry, but the mother and father have the right to have a life too), or put him to adoption from birth.
But I get they wanted to raise him, without seeing how much a child costs financially and psychologically. They also are human beings who sacrificed a lot, and they made mistakes, so I'm honestly pitying them a lot.
They did well to put Mokyeon for adoption, as he also deserved to be raised normally (they couldn't guess what would happen) and try to pull themselves together without that obstacle.
And trying to come back into his life show that they loved him, but yeah. They were too late, and it was up to Mokhyeon to choose what to do.