I disagree, OP.

If they don't let people know they are new, they won't know what to do in the various situations. I just ran a dungeon last night with a PUG and two of the four had yet to do it - I was one of those two. Because we spoke up, the other two told us what to expect and what to do. We completed it because we spoke up and we weren't surprised by anything which would have certainly killed us all.

If people are jerks because someone is doing content for the first time, the problem isn't the new person.