Alright, if you want me to elaborate for you......
1. You are advocating replacing a proven, top quality goalkeeper, with 57 international caps to his name and still in his 20's, with someone relatively inexperienced, who has played the grand total of 4 games in 2 seasons for his current club.
2. Joe Hart is arguably the best one on one shot blocker in world football, in the top half dozen (IMO) when it comes to the spectacular stuff, and at 6ft 4', a real physical presence in a very physical league. I too would prefer him to catch the ball from corners, but if you want to cite that (along with his supposedly suspect distribution - which I personally would call bullshit given that he only ever has a collection of diddymen to aim at) as grounds to get rid, then frankly I think you're certifiable.
3. Joe Hart is English. Our inadequate home grown quota has already led to us being held over a barrel once, when that bastard Milner played silly buggers over signing a new contract safe in the knowledge that due to FFP restrictions, we couldn't afford to offload him because of his nationality. Ditching Hart would pretty much leave us with Delph, Clichy and Sterling in that capacity. Quite apart from leaving us short on squad numbers, it would also make us vulnerable to legislative change dreamt up by rag c*nts like Gill and Dyke, the latter of whom would love nothing more than to up the home grown quota, a) because it would suit the rags, the dippers, the Arse and Spurs to do so, and b) because it would stiff us.
4. A lesser point, but Joe Hart is effectively one of our own. A big character who loves the club and who is (IMO) good for morale.
Is Joe Hart perfect? No, of course not. He drops the odd ricket, like the fuck up at home to Swansea or the soft scuffer he let in from Lallana recently, just like any other keeper, but that notwithstanding he's a fucking good goalie, who's saved our bacon on umpteen occasions. As priorities go, trying to find a replacement for him is pretty much second only to selling Aguero on my list. There, will that do for you?