It's a solid ship heehee ! ´>`
It's not my main ship, but I do have some theory supporting it! Here's the theory-- the two need each other very much, even with drastically different moral believes. Or maybe its because of the contrasted believes they need each other... assuming Kyle's always trying to put himself on a moral high ground, he needs Cartman to be there doing all the contrary things, and then fail, to prove him right. At the same time they're all clever people (to some degree), so maybe they'd admire each other's ability to achieve their goals, with different methods. Also, somehow I feel like Kyle might be a bit envy of Cartman, because of family issues, like, Kyle has a strict mom while Cartman can basically do whatever he wants. Also he might even admire Cartman's ability to express his desires and needs even though they're morally wrong, while Kyle himself have to be more restrained... These complicated feelings might cause them to get more attached to each other throughout the time ´>`