@Thomas,
Thomas, I see your point-- but I think that the carpet bombing metaphor is a little strong. Pick a whatever you consider justified military action (since you are using the bombing metaphor), and you will see that the whole nation is affected (not just people who support the regime).
Anytime there is a military action, or a political struggle, there are consequences that ripple beyond the target. That is the nature of battle.
This is a battle about justice; there are people and communities and principles that are threatened by this law. Many of us feel that this is important enough to fight strongly against.
The Arizona legislature is elected by Arizona. They represent Arizona. Arizona is responsible for them-- and Arizona has the only direct way to restrain their legislature. For Americans who are deeply angered by the actions of the Arizona legislature, we have no choice but to pressure Arizona.
It makes no sense to pretend that the residents and businesses of Arizona aren't responsible for their legislature and governor..
I am consciously separating the discussion between what is effective from the discussion about what is moral.
But the legislature, which represents the state and is accountable to the state as a whole, has taken an action that is deeply offensive to me as an American. I don't have any problem if Arizona, as the state that is responsible for their legislature, feels some pain in our attempt to force Arizona to reverse course.
Ironically enough, some of the strongest calls for the boycott are coming from an elected official (who happens to be Hispanic) from Arizona who is asking for help to oppose this law.