The Maesters wrote the Pink Letter

[AegonSnow]

• The Maesters don't want news of dragons, and may have have a hand in their previous extinction
  
• The Maesters probably similarly wouldn't want any superstitious stories about wights and White Walkers and Others.
  

• So, how best to get them out of the way? - Have a Maester Send a letter that sends the Lord Commander in offense to the Citadel into a situation that will put his very life and vows at risk: either way, either his enemies kill him, or his brothers of the watch do.
  

[Mladen]

And then NW would get a new LC, who will do the same as Jon. Spreading stories about Others, and asking for help. Not clever plan for such intelligent people, don't you think?

[otherbeef]

can never trust those grey rats

[Ser_Cortnay_Penrose]

The Maesters don't strike me as adequately stupid to fight the rumors of White Walkers and dragons rather than fighting/aiding the fight against Walk Walkers and dragons themselves. They hate and fear magic, true...so why sabotage the one guy trying to mitigate the oncoming invasion? And how could they possibly have the knowledge of Ramsay, Jon Snow, Stannis, Mance, Reek, etc. necessary to produce that letter?

[Ser_Cortnay_Penrose]

And how could they possibly know that the NW would end up killing Jon, if that was their game? Why not just send some assasin? Would probably be easier and mor ecertain to kill Jon Snow directly, if you think about it, rather than predicting the complex psychological domino effect that led to his death.