Security and knowing a street address really aren't issues. Think about the radio guy who got shot dead in Denver some years back or the stage hand shot dead at the Today Show which has the best security you can arrange.
A minister quoted in one of the CDT items put it pretty well. Paraphrasing, he said when people get mad at God for whatever is troubling them, and they're unstable, they are likely to take out their anger on the people and institutions which claim to represent Him.
When someone (a) has severe mental problems and (b) is trained from birth to believe a higher being is watching and controlling his every move, and (c) things aren't working as the guy thinks they should, then (d) he tries to get even. We all have a touch of (b) and (c) but most of us don't have (a) and don't get to point (d.)
But I'm surprised attacks don't happen more often.