Yeah, we all needed to discuss acronyms very badly.What if someone misunderstood our acronyms and wasn't able to ask for explanation!
You don't have to ban people from private conversations, but it's useful to have an option to votekick someone. If everyone (or x percentage) agrees you can get that person out. Then again, someone might get his / her feelings hurt, and we wouldn't want that on a forum.
The alternative would be to start a new conversation. However, maybe in a group of 5, someone still likes the person you just left out in the new conversation. He might add the poor fellow to the new conversation as well, which can get rather annoying. He might even do it on purpose.
I have no idea whether this gets logged or not, but at the very least I think it would be useful to show who invited who in conversations. In that case, you know what's happening and can react appropriately.