To be charitable, I don't think people are really saying "controller sucks, make it suck worse!" and then cackling madly while they barbecue a box of baby kittens and eat it in front of starving orphans. I suspect the opposition comes from two premises:
1.) As long as auto-aim exists for controllers, people will find a way to exploit it while using a mouse/keyboard, gaining an unfair advantage over non-cheating players in both control schemes.
2.) Even if they don't, the existence of controllers with auto-aim and mice with precision aim means that players are not on a level playing field. They'll have asymmetric advantages and disadvantages based on the hardware they're using.
I don't agree with point 1, as I've
outlined at length; I think there are effective technical solutions that can contain the problem to, in the absolute worst case, be no worse than what already exists on the console platforms. (Which demonstrably hasn't destroyed or dramatically unbalanced PVP on those platforms.)
Point 2 is a harder thing to argue because it's effectively a moral argument, a sense of what
should be. The best answer I can give is that we already live in a world where people will have asymmetric gameplay experiences based on the hardware they choose to invest in: a gamer with a top of the line rig playing in 4K at 144Hz is going to have a significant PVP advantage over the poor schlub running at min spec who struggles to get 30Hz at 720p. The PC is not the platform for "everyone gets an identical experience"; if you want that, you should be playing on console.
From my perspective, Destiny was a console game which has been ported to PC. It was designed first and foremost to play with a controller, and the mouse/keyboard support should be integrated with the objective of balancing it against controller play; taking the attitude that controller play should be crippled or eliminated because M/KB are "the real way to play FPS" seems both parochial and incredibly smug, given that PC gamers are the newcomers from the viewpoint of Destiny veterans. I'd prefer to see the controller scheme that works on the other two platforms left alone, and whatever balance changes need to be made to bring control scheme parity be made to the new and platform-unique mouse aiming scheme.