I used to hate cena but that was then. Its not Cena's fault, he has no say, you can't blame Cena for shitty storylines or PG. I have lots of respect for what Cena has done for the company, he is very dedicated, the guy has a great heart and does charity. Cena is truly a hero, he doesn't deserve the shit he gets, he's a great guy and I'm sure there is a lot we could learn from him if we knew him personally.
It was WWE that made Cena change his character from a thug to the marine super-cena we know today, not cena. It was the management and creative that pushed him down our throats, cena didn't even get backstage power till recently. The guy has paid his dues, FFS he lost almost all the matches he was in during 2002-2003... he lost to Angle, Jericho, Lesnar, Eddie, Undertaker, Big Show. He didn't start really winning important matches till about early-mid 2004 when he recently turned face. He won his first ever championship almost 2 years after his debut, and won his first ever WWE title almost 3 years after his debut.
They started making him destroy everyone in 2004 because that was the same time when Brock, Rock, Austin, Foley, Goldberg all left the company. They had to push someone very young and deserving, so they pushed Cena on SD and Orton on Raw (whose spot Batista took over in 2005 since Orton was very immature that time & WWE didn't trust him)