What am I missing? Sullinger has some potential, but so did Gerald Green. What do people see in Sullinger that suggests that he holds more value than an above-average starting center?
I don't think that a Gerald Green analogy is apt. Sully is partly potential, but Sully actually knows how to play ball. He's earning time, playing like 18 MPG as a rookie on a Doc Rivers championship contending team, which ought to merit some sort of trophy.
We know he can score, he can rebound, he has range, he is a good passer, he doesn't turn the ball over, he's smart, he's picking up the D, he's taking charges like a boss. These aren't things he might do, these are things he DOES do, we've seen it in actual NBA games. That's not to say he doesn't have obvious downsides, since he does, but there you go, not really a GG in my opinion.
To your original question, I think people are just overly attached to him for non-business reasons. He's as tradeable as any other asset on the roster. This poster is not gonna disparage anyone who gets excited about a promising young rookie, though.
I'd personally be OK seeing Sully go if we got value back. Sideshow Bob would be awesome, so would Gortat.