1. In-character, the Faceless Prince is
explicitly against cognitohazards. It's their mechanical Fear, so they will take what actions they feel they need to to prevent them from showing up. Furthermore, as a knowledge and trade god... well, anything that drives people insane rather limits their ability to both learn and to interact with others in a functional manner, therefore tanking his influence among mortals.
2. Out-of-character, you are not the first to try to drive everything insane and under your control, and frankly, it is an archetype that I have become
exceedingly tired of. It's not fun to play against such people, as you basically have to decide between letting them do their stuff without interference (in which case you end up losing assets from the passive addiction/madness/
whatever effects they set up everywhere), or spend a bunch of your resources stopping them from doing that (less risky, but expensive).
EDIT:
What's Shinka's excuse?
Why do I need an excuse to protect my interests? I don't want everything to be corrupted and twisted to someone else's intent, so I made a thing to help prevent that.
PROTECTING your interests? YOU MADE JACK SHIT WHEN I DID THAT. Nothing would have even happened to you. If anything, you should be on my side. Corruption brings violence which brings competition which is ONE OF YOUR SPHERES
The stuff you're setting up is persistent. It doesn't matter if somebody doesn't have stuff around when you do it; countering your stuff is pretty much essential to making sure that you can ever definitely have anything in the material world.
Also, if I'm not forgetting, you specifically said that the insanity twists people to
your end. Also, insanity and violence are very much not the same thing, and frankly, in reality, most insane people are more likely to be the victims of violence than the perpetrators. So no, Spin does not really have a particular reason to be on your side unless they want to be.