The mods hate it because the API will take away their power, and will subject them to the will of each individual community. It will also force them to interact with the community on a regular basis, which also forces them into the limelight. It's also going to effectively limit them to one or two subs at the most that they can moderate. Lots of mods are going to get 86'd by the various communities as soon as it get implemented.
Basically, reddit mods, despite being free workers, are addicted to the power they think they have over each sub-reddit. It's so bad that it's a meme. The mods screaming the loudest are the ones that are afraid of being voted out by their communities. There was one who posted how he was a shepard to the flock of his sub-reddit, when all he does is clean up spam.
All in all, I can't wait for this API to be implemented.