I think that it is the essence of human culture to teach and share knowledge. An important part of teaching is inspiring curiosity. Knitting and crocheting in public inspires such curiosity. It is a good thing.
I can not see any problem with cable needles or short little sock needles - anywhere or anytime. Some needles might click, and those would be fine at a rock concert but maybe not at a chamber music recital. At a lecture, I do not see that knitting is any more distracting or bothersome to others than taking notes with paper and pen. I do not see that cable needles are any more dangerous than a pen and notebook on a bus, train, or plane. Moreover, however dirty some yarn may be, I do believe that most yarn is relatively sanitary in comparison to the fixtures (door handles, bar rails) in a public hall that has been recently touched by many hands and everything that floats in the air around an assembly of people.
Aaron