I think you're both getting a bit confused as to why little Willy has been playing in the cup games. It's not because he's our "club keeper" he's a keeper who plays in the cups, and therefore is guaranteed to start in all of the cup games. Such a thing doesn't exist, it's been invented by the overly sentimental on here.
There reason he has been playing in the cups is to keep him fit and sharp in case Hart gets ruled out and the team needs him. The best way to do that is to play him in competitive games. The lowest risk competitive game for him to play in are the cup games.
The reason we wan't to keep him match sharp is because that's what is best for City. If Hart gets ruled out it's better to have a keeper who has played recently, who's match fit and sharp. That will give us the best chance of winning trophies.
The purpose of the team and the squad is to win as many games as possible, and ultimately win trophies. We've got a golden chance to do just that on Sunday. We should play the best team, that makes the most sense.
People saying Willy should play because he's "the cup keeper" have either got a bit carried away with what a "cup keeper" is, or they are being overly sentimental about hurting little Willy's feelings. He's a big boy, he knows he's not as good as Joe Hart, he'll get over it.
Hart has to start.