You certainly don't fault Melo for much, but always fault Phil, KP and others, HOF. You pretemd as if Melo is being vilified when he's a 25M a year player who is supposed to lead a team to the playoffs. When Melo gets paid $5M a year, I'll put him on the same terms as players who are.
He's not been the player the Knicks hoped he could be when they traded for him. He's basically a Robin, not a Batman. They tried to make things happen with him as a Batman, but he is not able to. Some players can not win being a Batman. Some players can. Think about CP3. He's always making his team better. Every team he's been on plays better with him.
Melo is a player who is a very good scorer, but neither makes the offense or defense shift to a degree that results in major impact. The team needs to get a point guard, or a guard that can be in the Melo role. Highest usage player. Only this player passes, finds open players, and is the one that makes the offense go, the engine. It won't be easy to find that player, that's for sure.
And no KP is NOT that player. No one said he is. What people are sayiing is that if Melo is traded and KP is forced to create more shots and learn how to play better in the post by force, even if the team loses 60 games, it's not a bad thing in the longrun. KP will not likely be better than a Robin himself. Even Phil doesn't expect more than Pau Gasol (who was a #2 on a ring team in his prime) Where I think KP has elite value is rim protection. In his prime/peak, I hope KP can change the way the team can play defense. He won't be a James Harden, Russell Westbrook, MVP level player who is the engine off the offense.