Although MA Senate Bill 661 is entitled "An Act relative to Common Defense" if enacted into law it would actually bring more violence to the "commons" than already found there.

Why? Consider the following:
--first, Senate 661 would expand the existing common law right of self-defense well beyond protection of property, self and others in one's home by making it lawful to kill or injure another in "any place where they have a right to be"--including but not limited to, bars, sports arenas, concerts, etc.
--second, Senate 661 would make mortal combat the first response to any and all PERCEIVED threats regardless of whether there's a reasonable basis--i.e., don't call shooter dim-witted or worse, mentally deranged; just say s/he felt threatened, and Senate 661 would provide a "lawful defense."
--third, much like its prototype--Florida's now infamous "Stand Your Ground" law, Senate 661 would preclude the "arrest or prosecution" of anyone asserting a claim self-defense on this basis.
--fourth, much like its prototype--Florida's now infamous "Stand Your Ground" law, Senate 661 would preclude the revocation of firearm license(s) issued to anyone relying on it to assert a claim of self-defense. This is where its companion bill--H 1568, "An Act relative to Civil Rights and Public Safety"--would really come into play.
--fifth, Senate 661 would not only prevent criminal charges from being filed, it would foreclose any and all civil suits that might otherwise when a claim of self-defense fails after trial.

But don't take our word for it. Read it for yourself. The full text of the bill follows:

Bill S.661
An Act relative to the common defense.

By Mr. Brewer, petition (accompanied by bill, Senate, No. 661) of Beaton, Frost, Golden and other members of the General Court for legislation relative to the common defense [Joint Committee on the Judiciary].
Sponsors:

Stephen M. Brewer
Status: Referred to Joint Committee on the Judiciary

SECTION 1. Chapter 278: Section 8A. Killing or injuring a person defense of self or others;

Section 8A. It shall be an act of lawful defense if a person, who is an occupant of a dwelling or in any place that they have a right to be, used deadly force, or less than deadly force, if he or she acted in the reasonable belief that an assailant was about to inflict great bodily injury or death upon themselves or upon another person who also had a right to be in the location. There shall be no duty on a person to retreat from any place that they have a right to be. An act of lawful defense as outlined in this section shall not be cause for arrest or prosecution. Further, an act of lawful defense under this section shall not be cause for the revocation of a license issued under sections, 122, 123, 129B or 131 of Chapter 140.

SECTION 2. Chapter 231: Section 85U. Death or injury to assailants; liability of defender

Section 85U. No person who has committed an act of lawful defense as outlined in section 8A of chapter 278 shall be held liable in an action for damages for death or injuries to an assailant.

http://www.malegislature.gov/Bills/BillHtml/9011?generalCourtId=1