There have been plenty of ships in the Walking Dead, some good, some bad and some very very disturbing (I'm looking at you Cluke). So, what encourages you to support a ship and what discourages you to support a ship (If you ship at all, that is).
Weirder the better
What encourages me is the characters involved and how well their chemistry works. Javi and Kate can have a humorous relationship depending on what you say. Clem and Louis are the same on this regard. Ex. When they're on their "date" Louis is just being himself and Clem can't help but smile as he humors her. Clem and Violet have a more serious but very sweet relationship. Where Louis is open and comfortable, Violet slowly pulls back her many layers; revealing someone who wants the chance to love someone and to be loved herself.
A ticket from a ferry.
I see it as a funny meme we bitch around to piss off other people who don't like the ship at all, just for fun.
It makes the game alot better, making you actually care for a character.
I think it's a little unclear where the frame of reference is.
Romantic chemistry is an absolute must have for a ship. I've seen loads of ships where romantic chemistry is thrown out the window from across many different games. A turn down for me is if a character is forced into a ship that contradicts their sexuality (e.g. a confirmed straight character forced into a gay relationship or a confirmed gay character forced into a straight relationship).
Chemistry is definitely important. You mentioned Romantic Chemistry in one of your comments, but I'm thinking less about the Romantic side and more about the Personal aspect of it. Shipped characters need to have some level of commonality to them for it to work. Similar Mindset. Similar Background. What discourages me is when the ship is rushed, forced, poorly written, or "Doesn't make a lick of damn sense," as Kenny would say.