Good point, but, it happens. People occasionally make mistakes, even in professional organizations (I know from personal experience making them). I didn't write back myself, because I was confident many others would. Over time, I have gotten very good about using bcc and not cc, but it took some time to really get the habit ingrained. I counsel patience.
I received that email also, and immediately wrote back to its sender, noting what a troubling error it was. A breach of privacy to say the least.
There's nothing that can be done about it now, but it's not the sort of thing I expect from a professional organization. Many of us go to great lengths to avoid our emails becoming publicized, and it's quite troubling that this mistake occurred.
