If the trade package is #1 for #3 and LA2018, it's a no brainer for me.
Fultz isn't a lock star, Ball isn't a lock star, Jackson isn't a lock star. You are getting a kid who could be Michael Jordan, Michael Beasley, Len Bias, or Greg Oden.
By swapping 1 top 5 pick for 2 top 5 picks, you are doubling your chances of landing Michael Jordan. It's called diversification, and it's what brilliant investors have been doing for a very long time. That's what a draft is. You are investing in a player.
Let's say Celtics do this deal and sign one of Hayward or Griffin, you would have a team structured something like this
Guards: IT, Bradley, Smart, Rozier
Wings: Hayward, Crowder, Brown
Bigs: Horford, Zizic, Yabusele
along with 3 top draft picks over the next 2 drafts.
2017: Ball or Jackson
2018: 2 of Porter/Ayton/Bamba/Doncic
This allows you to compete NOW on the off chance of an injury, you get a free title while developing your rookies to compete in 4 years when GSW/Cavs are slowing down.
Let me put it another way: What are the odds that both (Ayton) & (Jackson) are combined worse than Fultz?