On the day that George Zimmerman made his first appearance in a Florida courtroom on charges of second-degree murder, a group of civil rights advocates in Boston called for the defeat of a state Senate bill they’ve compared to Florida’s “stand your ground” law. “If a law like this passes, what you will have is the last man standing tells his version,’’ said Larry Ellison, a Boston police officer who is head of the Massachusetts Association of Minority Law Enforcement Officers. “We can work this out without a new law that puts more guns in people’s hands who are not trained in law enforcement,” he said.