A major airport and the entire rail system of the city was shut down. A lot of damage was done. And, of course, a bunch of people died from something not many signed up for.
Driving a car at least gives you the opportunity to reject taking on the risk.
The fabric of society is based around us not shooting each other/ blowing up trains. Every event like this (or, say, some countries bombing out neighborhoods in other countries) makes it harder to rely on the idea that this sort of thing doesn't happen.
Acknowledging that this happens because of conscious policy decisions by many people is also good.
There's absolutely nothing inevitable about these kinds of attacks. We could bring this sort of event down to a number real close to 0.
Not to mention that it's possible to worry about car crashes and terrorism at the same time