We're all guilty of it. Hitting the reply all button, under the thought that a friend of yours is a friend of mine. And some people don't mind this. I know I don't, but I like to be included. I like to think that I am part of the conversation even if I don't join in.
Yesterday, my sister sent out a message urging everyone to contact their Senators regarding the gay marriage thing. Someone replied all expressing her opinion about it. Since it was contrary to a few other opinions, there were a few responses to that. Then people started requesting to be removed from the list.
The bad part is, that the reply-alls continued, without regard to those people's requests. I've seen it happen among my friends. Some serious flames were ignited once, and I'm not talking about the blue kind. it got kinda ugly. It was all, don't talk to my brother that way, hey you've insulted my uncle, you're all jerks...I hope this doesn't happen this time, although the last message came through all caps. apparently, he was really trying to get his message accross, which is understandable because it was his second request.
So I urge you, if you use the reply all button, please delete the names and addresses of the people who either, request to be removed from the conversation, or, you don't recognize them. I remember once I misspelled (no, really??) an email address and all my friends and I were discussing poo. to the amusement of a rather nice fellow in Mexico who didn't know any of us.