Security at a class D tower

I toured the new state of the art tower at Addison airport last week and
was struck by all the security measures they employed.

The entire complex and parking lot was surrounded by a dense wrought iron
fence with a nasty "fish hook" shaped sharp pointed curve at the top. An
intercom opened the gate. The entrance to the tower was an interlock of
bulletproof glass doors that locked you in a holding area until someone
checked the video camera and buzzed you in.

I assume this is all a reaction to our new terrorist threat, but I haven't
been able to come up with any reason for all that security. Let's say
some terrorists took the tower, what's the worst thing they could do?

--
Dallas