The thing is though - all these people that hate him (and I'll actually include myself) will probably become his biggest fans when he finally turns heel.
This is how most everyone hating on Cena is feeling, we're all just waiting for that moment when he's in the ring with Orton or Daniel Bryan or some other mid to upper level face, when he just turns and snaps on the guy. That moment when all the kids freeze and don't know what to do and all the haters switch and instantly start cheering Cena. I get the feeling I want to cheer Cena, but not this Superhero Cena. I want him to become heel, no doubt. I am also willing to wait another year or more until this happens. You have to have someone who can take his babyface spot and surprisingly the only guy who can do that right now would be the Miz and that would take complete role reversal, which wouldn't fit yet. Maybe in the future once people begin to realize Miz is a real threat and he starts getting the cheers like Orton did that switched him to face, then maybe you'd have a chance, but right now there is no ability to switch Cena to heel and not be hurting.