The idea that Smart is better than Okafor is laughable.
Smart will either significantly, and I mean truly significantly, improve his offense, or he'll be nothing more than a defensive specialist for his career, because his offensive game (in an offense-led league) is atrocious. Okafor is already a starting level player who's shown flashes of being an all-star caliber player.
Philly would be foolish to trade the two even up, and Boston would be foolish not to. Philly will, rightfully, ask for more. I just wouldn't give up Bradley, Horford, Brown, Crowder, Thomas, or the Brooklyn picks in that trade. Pretty much everything else can go.