You're looking at it from a fans perspective. Take the football side out of it... you're asking an employee to possibly give up some of his future earnings so his soon-to-be former employer can afford to pay someone else?
I get the "fond feelings" stuff but any person is entitled to earn what they can, and shouldn't be made to look bad for doing so.
Don't forget, it's a 2 way street. Any club can, and do release players at the end of a contract against a players wishes.
I want Sterling to stay, or I would prefer money for the club if he goes, but the way you're speaking about it, he'd be 'wrong' to see out his contract (and will slag him off if he does)