ROFLman, I'm not sure if your question was sincere, but I assume it was?
In my opinion, this is what is going on:
Representative Marty Walz, D-Back Bay, wants to keep her neighborhood protected from over-development. A laudable goal, in fact, since what makes the Back Bay the "Back Bay" is its beautiful architecture and design.
Unfortunately, she has taken this to the extreme; now she is nothing but an obstructionist, against anything and everything that will change the neighborhood, at all.
The city of Boston has seen many proposals for mid-to-high rises during the past decade. Several of these buildings have been proposed in and around the Back Bay. The Boston Redevelopment Authority is ready to give approval to proposed projects including an office tower on Prudential Plaza and a 47-story condominium tower on an empty lot owned by Simon Properties on the corners of Stuart and Dartmouth streets. It has already approved a ~22-story apartment tower on Exeter Street, just two blocks from Copley Square.
Rep. Walz sees what is happening and is not pleased. In a normal world, she would be helpless to do anything about it, but in Boston, things are different, with the state having meddled in the city's affairs for well over 100 years.
Seeing herself as the champion of all that is good in the world, or at least her neighborhood, she has taken it upon herself to usurp the city's control, and decree by state law what can and cannot be built in major parts of the downtown. That is the goal of her bill, which would outlaw tall buildings on the Rose Kennedy Greenway, Copley Square, and the Fens. (She says she's not "outlawing" anything, simply codifying current city zoning regulations for the area.)
Simply, she doesn't trust the city's leadership to do what is "right" and wants to do it herself.