Now, at the time I'm writing, we don't know whether the arsonist was targeting the NAACP or the store next to it. Usually, terrorists take credit for what they've done with press releases or graffiti. But let's assume that the target was the NAACP office and the bomber was offended by what the NAACP believes. Does being offended give you the right to silence the people at whom you're taking offense?
Stephen Fry has a fine answer:
Offended people love to share the fact they're offended. They forget that the right to free speech protects their right to tell anyone who will listen that they're offended.