I don't think it's a danger. First, how would they know those are newbies? Second, I think you underestimate the 99% of players, who wouldn't do that and, instead, would help those players.

Also, members of the newbie cabal could be PK-protected until level 30. With the restriction that they won't be able to join any other cabal. So such restriction wouldn't be abused by vets.