I wouldn't describe this as involuntary. The losing party can simply leave (be banished) at any point, rather than face the consequences prescribed by the group. There's no threat of violence or imprisonment, at least as described in this article.
If you take "involuntary" to mean "faced with consequences for one's actions within a group", then maybe it is involuntary, but that's not how the word is used with relation to anarchism as I've seen it.
If you take "involuntary" to mean "faced with consequences for one's actions within a group", then maybe it is involuntary, but that's not how the word is used with relation to anarchism as I've seen it.