Martin, the real son.

I agree. He was a bit of a monster.

He was supposed to represent all that was wrong with humanity.

Rare to see such a malevolent kid from Spielberg.

Martin ruined everything.

The kid and the mother were annoying as f...

In a way, it was Martin who propelled the story forward.

I mean, wasn't it Martin's idea to have his mother read Pinocchio to both him and David, sowing the seed in David's mind about becoming a real live boy?

Martin displays the angst of his dwindling species, the angst of a child afraid of being replaced by a 'perfect' android, and the neurotic confidence of a son who knows he's the only child his parents are ever going to have. He's their Golden Child, their Only Ever, and he may even understand that as a person he's a bit of a sh*t. Unfortunately that all makes him very much the product of his parents. David is who David is, because his 'parents' made him that way. The same is true for Martin.