I don't think that John Cena is nearly as unpopular as some of the people on hear would have you think. The majority of WWE fans are Cena fans for the most part.
The fact is that WWE caters to the average fan and younger kids, and despite what alot of hardcore wrestling fans think, there's nothing wrong with that. When Cena comes out for RAW on Monday's, he gets the biggest and wildest pop out of anyone on the roster. The only guy that I can think of in the entire WWE that can rival him in terms of pure fan reaction is Jeff Hardy.
Just look at the numbers. Ratings for RAW have been higher since Cena has come back from his injuries, and his merchandise outsells everyone else in the company by a long shot. The people that despise Cena so much are mostly people that are super hardcore fans and make that a major priority in their lives.
Think about it for a second. Everybody has wrestlers that they like and dislike. For example, I'm not Triple H's biggest fan. But no sector of wrestling fans are as vocal about their disliking of a guy that Cena-haters. They really do go to incredible lengths to let you know that they don't like John Cena.
That's fine, everyone is entitled to their opinion, but a lot of people get way to into it.