It's a serious point. Suicide bombers don't target airports out of some strategic desire to prevent air travel. They bomb airports because there are a lot of people there.

You can put all the security measures you wish in place, stretch out the lines, distribute the people as far from one another as possible ... and all you'll do is reduce the attractiveness of the airport as a target.

So then people looking to incite terror will bomb a church, or a school, or a sporting event ... there will always be places when the crowd is big enough to make a point, and you can't just eliminate crowds.