[h2odragon]

So many places with obtrusive security presence, security checkpoints, etc; still have a side door propped open around back somewhere that lets you wander through the "controlled" area freely.

The "defensive design" things like bollards and big planters that block walkways are like rung 1 (or 0.2, perhaps) on the "defensive earthworks" ladder. Its a well studied field and there's counter-actions available for most of that kind of thing. An attack may become more expensive to prepare and require more resources in flight but the bollards and defenses can be hit first and removed.

Judging by the results off all the upgraded security measures since 9/11; we can see what is actually feared.