I think you might be looking at it the wrong way - consider it for a while. The target: the people. Any people. Men, women, kids. Symbolic? Perhaps not. But the act is a statement in itself - "you believe you're safe - you're not". Any time you're at the mall, or a sporting event, or an amusement park, or have taken your kids to the playground, you're potentially within the range of someone with a backpack full of explosives. How's that for terror?