Not rating the guy: Tebow has a terrible throwing action, it's improving, but if you watch the ball when it leaves his hand then is isn't in a 'spiral' (nose first in an arc while the ball spins about its axis) like you see from the best QBs like Drew Brees, Tom Brady, Aaron Rodgers & Payton Manning. He has great feet, is difficult to tackle and speed and gets things done, so fair play to the guy (I'm a huge Steelers fan so that hurts me to say it).
'Hating' the guy: He was hyped all the way through college and even more so now. He's being helped massively by a very good defense and good O-Line (the fat guys who block the defenders and stop the QB from being tackled). He's got a lot of lucky breaks too so the press coverage saying he's great is quite grating. Also the religion thing means he's a Fox News darling, enough to turn anyone against him. It's not his fault, it's more a resentment for the hype.
There's also some apathy towards Sidney Crosby in the NHL, but unlike Tebow, he's an absolute superstar and has captained his team to a championship, proven himself as one of the best in the league and Canada to Olympic gold; so it's not unique in america for random 'I absolutely love the guy' vs 'I hope he loses' scenarios.