I'm not entirely happy with this decision myself, but there really isn't any middle ground. I thought Guest Chat was a way to be more inclusive and build the OtC audience. I thought by and large we handled the occasional troll guest well and that the majority of the guests were a net plus for the cast.
However, I'm aware that my perceptions aren't always shared by other people, and that I can be consistently wrong in certain situations. I think I may not fully understand how much the occasional troll, or the possibility of a future troll, can adversely affect other people's comfort level with the cast. I probably underestimate the extra burden I put on the mods by allowing guests. I think I overestimate the value guests have brought to the cast in actuality, and I haven't fully appreciated the unfairness to the regular signed-in viewers of giving equal status to anonymous, often one-time viewers.
So, guests: if you want to chat, you're going to have to sign in. OtC won't be quite as different as it was. My sincere thanks to all my friends who provided input on this issue and who have put up with my public decision-making process. And now I'm moving on.