Fortunately, my initial reaction ends up being extremely simple and should not take long to unpack. No, we should not be shunning anyone for the "crime" of saying things we do not like. Efforts to do so are not something I'll support.
Like Conservative Skeptic and many others, I find some of what PZ Myers says to be embarrassing, counterproductive, or just plain idiotic. But that is okay. He gets to say things like that. Not only am I not interested in trying to stop him from doing so, but I do not see myself as having any right to try to stop him from doing so. I don't have to agree with what he says or enjoy hearing it in order to defend his right to say it. I also don't have to listen to it if I would prefer not to do so. I can also respond to anything he's written, explaining why I disagree.
I recognize that there are different definitions of shunning and that some people seem to regard it as an individual decision to avoid someone. I do not care for this definition because shunning strikes me as an inherently social act that it extends well beyond my making a personal decision about whether I want to engage with someone. In other words, I don't think I am capable of shunning someone all by myself. If I was, then I'd see no difference between shunning someone and deciding to stop reading their blog. There are plenty of blogs I stop reading, and I would not agree that this constitutes shunning their authors.
I believe that shunning someone would involve my joining with others in making an effort to persuade others to stop reading someone (or inviting them to conferences or whatever other way we are trying to limit their influence). That is, I see shunning is an organized effort to marginalize someone (e.g., decreasing their audience, their support, their reach, etc.). And defined this way, shunning is not something I'm inclined to support.
So, do I think that other atheists and skeptics should shun Myers? No. I'm not interested in attempting to purge ideas I do not like. Anyone who does not care for Myers' shtick is free to stop reading him or to criticize his ideas to help others see what is wrong with them. Doing so might even prove to be beneficial to oneself and others. Anyone who regards Myers' ideas as toxic is free to explain why and provide alternatives. If the fact that he is invited to speak at conferences bothers someone enough, this person is free not to attend or to attend and simply skip Myers' talk.
I have neither the right nor the inclination to push others to hasten Myers' marginalization. It seems to me that he's doing a perfectly good job of that on his own.
If you think I'm wrong here, please feel free to explain why in the comments. If you believe you have a solid case for why we should shun someone because we disagree with their ideas, I'm interested in hearing it.