Kathleen Taylor, the executive director of the ACLU of Washington, posted on the organization's blog today about why they're suing the county, which banned bus ads critical of Israel:

I have been warned that the Mideast Awareness Campaign bus ads could end up covered with graffiti or that the buses’ operation could be disrupted. These days, people are angry and scared for a whole host of reasons — the economy, war, terrorism, and health care, to name a few — as well as Mideast politics. In a democracy should we stop talking about important policy issues when the terms of the discourse make others very uncomfortable? Can speech be limited if it might provoke someone to commit an act of violence? More broadly, how can we keep America safe and free?

As we consider these questions, let’s keep in mind that mild speech doesn’t need protection. It is when we are faced with controversial speech, speech that is intensely upsetting, that our adherence to the First Amendment is most important.

Instead of banning politically charged statements, King County executive Dow Constantine—who is behind the Constitutionally dubious ban—and local government need to "focus its considerable law enforcement resources on the people who are threatening the violence," says Taylor.