So many flags are at half staff- why?

While driving about, I noticed so many flags at half staff.  What gives?

Something similar happened after 9-11, when so many people put old glory on their cars.  The left at that time lamented the "patriotism run amok".  I suppose this must be the left's answer to that- grief run amok.  Anytime there's a tragedy to exploit, we are encouraged to join in the spirit of victimized outrage.