To be frank, some of the staff at US airports appear to have an IQ barely above imbecility. I've been in the US four times, and nowhere else have I seen such unfriendly, unhelpful, and downright hostile personnel than at the airports. A man whose only job appeared to be holding a sign pointing to a gate refused to show us the way to the toilets. Another man went through our bags before we boarded and found the remains of a coconut which we'd intended to eat on the plane; he turned to me (I was 12 at the time), said "you must be a real idiot" and threw it in the garbage. If people like that are employed by the TSA, I'm hardly shocked that situations like the one with the little girl make the news every few weeks. If those dimwits don't know how to properly interact with passengers, put them in a position where they don't have to, or don't hire them.
Last year, we did a trip around Iceland. Before our return flight, when we waited at the security check, we found that we still had some 2 liter bottles of lemonade in our bags. So we started chugging away (don't like to waste food), and a security guy came up to us. He told us to relax and take the bottles on the plane. "This is Reykjavik, not New York. Have a nice flight."
Keep in mind that some of these TSA agents are actually cops that may have been fired for whatever reason by their jurisdiction, and they'd do anything just to make a get by in this economy and retain their experience at the same time. Some cops may actually start out as TSA agents instead of serving in the military or, for heaven's sake, being 'mall cops'.