Why Medford is divided about the Green Line extension; Will Medford become Somerville or Arlington?

Why Medford is divided about the Green Line extension.    Some look forward to higher property values others worry about gentrification, crowding, and noise.  Will Medford become Somerville or Arlington?  And behind all those issues is frustration that residents have "been given little chance to provide input to a project that seemed ordained by officials elsewhere."