I know Carmelo Anthony elicits strong emotions from people. Let's try to put those aside and consider:
BOS sends expirings, young talent, picks:
Evan Turner
David Lee
Tyler Zeller (or Sully, if they want him)
James Young (or Terry Rozier)
BOS 2016 1st, DAL 2016 1st, potentially BKN 2018 1st (2nd rounders as needed)
NYK send Carmelo Anthony
http://espn.go.com/nba/tradeMachine?tradeId=gvc2eqxWhy New York does it:
They get Melo off the books starting next season, as Lee, Zeller and Turner are expiring deals they can choose to keep or not. That gives them more flexibility to nab a star next summer, plus their picks give them a better chance to rebuild. Their future looks better after this and, honestly, they weren't making the playoffs this year anyway.
Why Boston does it:
Consolidate frontcourt, add a proven superstar who is talented enough (and old enough now) to slide into a system. This I believe. Melo always brought it to the Olympics and his game ages well - think Paul Pierce. He makes us a sexier destination and we keep our 2016 BKN 1st. This season we become a legit playoff contender for the ECF at best, and at worst we become a tough out. Our future is intact.