The case against Okafor is strong. He could become a volume scorer, but at the expense of team spacing and defense. He has no outside game at all, and will always be a below average defender.
Everyone bemoans the lack of a star, but we are two athletic, defensive minded bigs away from having the best defense in the league, all with players just entering their prime. We can achieve that without any luck at all. I wouldn't sell that out just to get Okafor's offense.
Okafor is going to be a good player. Al Jefferson has been a really good player. Flaws exist, but that doesn't mean he won't be good, he could very well he an all-star one day.
Thing is, the #3 pick or a package built around it is the best chance we have of laying the groundwork for a contender in the future. And much like Al Jefferson, even though Okafor could be an all-star level talent, it's very unlikely you can build a champion around him as the centerpiece, which you would have to do because of his skillset.
People shouldn't confuse not wanting to trade our highest pick in over a decade (plus possibly more assets) for Okafor with saying he's not going to be a good player. He is going to be. But would you trade #3, #16 and Smart for a 20 year old Al Jefferson or Brook Lopez? I wouldn't.