What do you think they are trying to do in those hospitals? Gain info about how to sabotage treatment? Plant supergerms? Why aren't these intruders being arrested and questioned......?
I've thought about that myself. Most people there are incapacitated and generally unable to fend for themselves. People remaining in the structure (doctors, nurses, orderlies, cafeteria workers, gift shop workers, volunteers and hospital visitors) are valued community members. A seige is one possibility. The number of people sitting in an average emergency waiting room alone is generally quite large. Easy to secure entrances and exits and with a large number of patients all over the hospital premises, the potential prevention of penetration from exterior attack.