If the full extent of what Greg is saying about his upbringing is true, then he didn't have a normal childhood - he had a regimented one, where he was an extension of his parents' wills. He specifically said that everything he liked, wore or wanted was always wrong, which implies a controlling household beyond the pale of normal childhood, even if it's frequent in society. His activities were things his parents wanted him to do, and even music was limited.
Whether or not he's being completely truthful, this is his only point of reference from his own childhood, and more importantly, would have been at the time his son was coming into existence. He never wanted that life for Steven, because to his experience, his childhood was terrible, and nothing really invalidates that experience, even if other people have it worse. He also couldn't, at that point, have anticipated interstellar wars, alien invasions and so on, because his experiences with gemkind were very, very limited in the grand scope of things. After everything that's happened, he tries to fall back on the only things he knows from that sort of age, even if they're not as relevant as he hopes they would be.
tl;dr - shit's complicated.>>113781333
Well, looks like someone nailed it better than I could.