I just explained that in the post? Use in storylines. Cena as a character doesn't really make for compelling storylines unless the other guy feeds him everything-- Cena as a superman gone bad ruling the show is just good stuff.
Also the reaction wouldn't be the exact same.. Cena gets a mixed reaction leaning face now he'd get a mixed reaction strongly leaning heel then, cause as I said I expect the people who are chanting "Let's go Cena!!" flop over easier than the "Cena sucks!" chants. Like a lot easier. In fact I'm not entirely convinced most of the "Cena sucks!" people even turn over since I'm not really sure Cena's character being stale is their whole issue with him.
I was just saying that in principle a mixed reaction for the top heel isn't necessarily bad.
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I tried to have a fierce rivalry with SuperNiceDog, but he made me look worse than a GameFAQs Contest!